Water in glass
Rainwater harvesting with Sustainable technology: A look at the design, construction and operation of a small scale slow sand water filter. (Building a small slow sand water filter for individual use) 6  note 1






Introduction
Please note: I strongly suggest reading the  terms of use and license regarding the content of this site.

The slow sand filter projects documented on this website have taken place in the pacific northwest area of Washington state, USA. The first filter project (filter one) was started in early 2007. All of the projects are ongoing and will continue as long as the author is able. The water quality tests that have been done by epa certified testing laboratories are noted as such. The preliminary field tests are done onsite and are also noted as such. The researcher has a four year degree from the University of Washington (class of 2006) in environmental studies plus 35 years of experience in non-academic work. Chemicals used for drinking water treatment such as chlorine, or ozone that produce toxic cancer causing byproducts are not used in these filters. The longest running slow sand water filter project this site documents has been ongoing for six and a half years (it was started in the summer of 2007). It will continue as long as possible.

Keep in mind that "Backwashing" a biological sand filter will destroy it.; and that a biological sand filter is constantly full of water up to and covering the top surface of the sand inside by at least 1 inch or more - the sand must not be exposed to air.
Know that the content of this site will change considerably as this study continues.

Rain barrels are now legal in Washington state! For over 90 years it has been illegal to catch rainwater in Washington state.note 2 As of October 9 2009, catching roof water is no longer a crime! The department of Ecology in Washington state (the D.O.E.) has finally clarified the law so as to allow individuals to catch rainwater for their own use. (from this preceding link, click on the links at the D.O.E. site on the upper right hand side of their page that say "new" highlighted in yellow.)

So far work has been done on 10 different filter configurations. Five separate small slow sand filters are involved:

slow sand filter drawing
Filter one (external link)
slow sand filter drawing
  Filter two  
(float valve installed 2011-04-07)
slow sand filter drawing with float valve
    Filter three

slow sand filter 4 drawing
filter 4
slow sand filter 5 drawing
filter 5

FLOW SUMMARY FOR TESTED SUCCESSFUL DESIGNS OF SMALL SLOW SAND WATER FILTERS
See faq 31 for an explanation of flow rates
or the U.S.D.A. site has a good explanation of water flow through sand
Filter 1 (fourth configuration)*
input: roof water
using first flush diverter. 3 tab comp. roof.
top layer of sand .15mm effective size
bottom layer of sand:
non-graded. approx. .65mm effective size
electric pump recirculation at less than 1 L/hr.
container diameter: 23 inches
sand surface area .26791 sq m
container depth: 30 inches
Filter 2*
input: pond water
top layer of sand: .15mm effective size
bottom layer:
non-graded "fine" sand approx .30mm effective size
container diameter: 22 inches
sand surface area .2452 sq m
container depth: 40 inches
2010-09-16: this filter now
has a float valve installed

Filter 3 (with float valve flow control).
input: shallow well water
top layer of sand: .25mm effective size
bottom layer: 35mm effective size.
container diameter: 22 inches
sand surface area .2452 sq m
container depth: 40 inches
Date.
12 L/hr (10 cm supernatant water depth) (.045 meters/hr) no measurement no measurement 2008-01-02
3 L/hr (10 cm supernatant water depth) (.011 m/hr) 12 months continuous operation no measurement no measurement 2008-12-01
no measurement 72 L/hr (20cm supernatant water depth) (.286 meters/hr) 90 L/hr (16.5cm supernatant water depth) (.358 meters/hr) 2009-02-08
14.1 L/hr (10 cm supernatant water depth) (.053 meters/hr) 2 months running time
was totally frozen in Dec 2008 / Jan 2009.
42 L/hr (20cm supernatant water depth) (.167 meters/hr) 45 L/hr (16.5cm supernatant water depth) (.179 meters/hr) 2009-04-08
13.84 L/hr (14cm supernatant water depth) (.052 meters/hr) 40 L/hr (20cm supernatant water depth) (.159 meters/hr) 48 L/hr (18.5cm supernatant water depth) (.191 meters/hr)** 2009-04-26
13 L/hr (14cm supernatant water depth) (.049 meters/hr) 36 L/hr (20cm supernatant water depth) (.146 meters/hr) 45 L/hr (18.5cm supernatant water depth) (.183meters/hr) 2009-05-11
12 L/hr (14.5cm supernatant water depth) (.045 meters/hr) 36 L/hr (20cm supernatant water depth) (.146 meters/hr) 36 L/hr (18.5cm supernatant water depth) (.146 meters/hr) 2009-08-07
12 L/hr (14.5cm supernatant water depth) (.045 meters/hr) 36 L/hr (20cm supernatant water depth) (.146 meters/hr) 25.7 L/hr (18.5cm supernatant water depth) (.104 meters/hr) 2009-09-04
9 L/hr (14.5cm supernatant water depth) (.034 meters/hr) 22 L/hr (20 cm supernatant water depth)(.09 meters/hr)
added 48 liters of roof water from diverter output
28.8 L/hr (18.5 cm supernatant water depth) (.117 meters/hr)
added 48 liters of roof water from diverter output
2009-09-21
10.74 L/hr (14.5cm supernatant water depth) (.040 meters/hr) added 12 litres of undiverted roof water 22 L/hr (20cm supernatant water depth)(.09 meters/hr) (no significant change)
added 48 liters of roof water from diverter output
25.7 L/hr (18.5cm supernatant water depth) (.103 meters/hr)
added 48 liters of roof water from diverter output
2009-10-08
9.24 L/hr (14.5cm supernatant water depth) (.035 meters/hr) 21 L/hr (20cm supernatant water depth)(.086 meters/hr)
21.81 L/hr (18.5cm supernatant water depth) (.089 meters/hr)
2009-10-12
10.58 L/hr (14.5cm supernatant water depth) (.039 meters/hr) 20.57 L/hr (20cm supernatant water depth)(.0839 meters/hr)
source water changed to surface well
21.17 L/hr (18.5cm supernatant water depth) (.086 meters/hr)
source water changed to surface well
2009-11-05
9.00 L/hr (14.5cm supernatant water depth) (.0335 meters/hr) 18.95 L/hr (20cm supernatant water depth)(.077 meters/hr)
19.46 L/hr (18.5cm supernatant water depth) (.079 meters/hr)
2009-12-04
0 L/hr Filter frozen*** by below 0°C weather 0 L/hr Filter frozen*** by below 0°C weather
0 L/hr Filter frozen*** by below 0°C weather
2009-12-07
11.25 L/hr (14.5cm supernatant water depth) (.042 meters/hr) 35 L/hr (20cm supernatant water depth)(.142 meters/hr)
30 L/hr (18.5cm supernatant water depth) (.122 meters/hr)
2010-01-01
11.25 L/hr (14.5cm supernatant water depth) (.042 meters/hr) 27.7 L/hr (20cm supernatant water depth)(.113 meters/hr)
28.8 L/hr (18.5cm supernatant water depth) (.117 meters/hr)
2010-01-09
8.37 L/hr (14.5cm supernatant water depth) (.031 meters/hr) 32.7 L/hr (20cm supernatant water depth)(.133 meters/hr)
27.7 L/hr (18.5cm supernatant water depth) (.112 meters/hr)
2010-02-07
9.47 L/hr (14.5cm supernatant water depth) (.035 meters/hr) 24 L/hr (20cm supernatant water depth)(.098 meters/hr)
25.74 L/hr (18.5cm supernatant water depth) (.105 meters/hr)
2010-03-01
8.47 L/hr (14.5cm supernatant water depth) (.032 meters/hr) 24 L/hr (20cm supernatant water depth)(.098 meters/hr)
25.74 L/hr (18.5cm supernatant water depth) (.105 meters/hr)
2010-03-26
8.47 L/hr (14.5cm supernatant water depth) (.032 meters/hr) 24 L/hr (20cm supernatant water depth)(.098 meters/hr)
24.25 L/hr (18.5cm supernatant water depth) (.099 meters/hr)
2010-04-30
10.3 L/hr (14.5cm supernatant water depth) (.038 meters/hr) 29 L/hr (20cm supernatant water depth)(.118 meters/hr)
34 L/hr (18.5cm supernatant water depth) (.139 meters/hr)
2010-09-16
11.15 L/hr (14.5cm supernatant water depth) (.0416 meters/hr) 26.4 L/hr (20cm supernatant water depth)(.108 meters/hr)
28.2 L/hr (18.5cm supernatant water depth) (.115 meters/hr)
2010-12-19
16L/hr (14.5cm supernatant water depth) (.0597 meters/hr) 28 L/hr (20cm supernatant water depth)(.1142 meters/hr)
33 L/hr (18.5cm supernatant water depth) (.1346 meters/hr)
2011-02-06
12.2L/hr (14.5cm supernatant water depth) (.0455 meters/hr) 22.29 L/hr (20cm supernatant water depth)(.091 meters/hr)
27.23 L/hr (18.5cm supernatant water depth) (.111 meters/hr)
2011-03-08
13.56L/hr (14.5cm supernatant water depth) (.0506 meters/hr) 26.67 L/hr (20cm supernatant water depth)(.1087 meters/hr)
28.24 L/hr (18.5cm supernatant water depth) (.115 meters/hr)
2011-04-16
10.64L/hr (14.5cm supernatant water depth) (.040 meters/hr) 32.21 L/hr (20cm supernatant water depth)(.131 meters/hr)
31.86 L/hr (18.5cm supernatant water depth) (.130 meters/hr)
2011-07-02
16.14L/hr (14.5cm supernatant water depth) (.060 meters/hr) 38.71 L/hr (20cm supernatant water depth)(.158 meters/hr)
41.62 L/hr (18.5cm supernatant water depth) (.170 meters/hr)
2011-09-14
12 L/hr (14.5cm supernatant water depth) (.0448 meters/hr) 28.685 L/hr (20cm supernatant water depth)(.117 meters/hr)
32.8 L/hr (18.5cm supernatant water depth) (.1337 meters/hr)
2011-11-25
10.48 L/hr (14.5cm supernatant water depth) (.039 meters/hr) 44.31 L/hr (20cm supernatant water depth)(.181 meters/hr)
31.86 L/hr (18.5cm supernatant water depth) (.130 meters/hr)
2012-03-06
15 L/hr (14.5cm supernatant water depth) (.056 meters/hr) 58.42 L/hr (20cm supernatant water depth)(.238 meters/hr)
37.9 L/hr (18.5cm supernatant water depth) (.177 meters/hr)
2012-08-09
13.14 L/hr (14.5cm supernatant water depth) (.049 meters/hr) 42.85 L/hr (20cm supernatant water depth)(.174 meters/hr)
43.9 L/hr (18.5cm supernatant water depth) (.179 meters/hr)
2012-10-03
10.98 L/hr (14.5cm supernatant water depth) (.041 meters/hr) 48 L/hr (20cm supernatant water depth) (.196 meters/hr)
28.57 L/hr (18.5cm supernatant water depth) (.117 meters/hr)
2013-04-30
10.00 L/hr (14.5cm supernatant water depth) (.037 meters/hr) 51.4 L/hr (20cm supernatant water depth) (.192 meters/hr)
42.4 L/hr (18.5cm supernatant water depth) (.158 meters/hr)
2013-08-27
12.32L/hr (14.5cm supernatant water depth) (.046 meters/hr) 33.96 L/hr (20cm supernatant water depth) (.139 meters/hr)
37.8 L/hr (18.5cm supernatant water depth) (.154 meters/hr)
2014-03-13
FLOW SUMMARY FOR FILTER 4 AND FILTER 5 *
Filter 4 (3rd configuration)
.45 mm effective size bottom sand 600 lbs
.24 mm effective size top sand 80 lbs
dc pump is used to recirculate water
filters roof water from composition roof
sand surface area: .26791 sq. m.
container depth 32 inches
started 2011-11-01
Filter 5
.25 mm effective size bottom sand 700 lbs
.15 mm effective size top sand 150 lbs
filters roof water from composition roof
sand surface area: .2452 sq. m.
container depth 40 inches
started 2012-05-01
Date
30 L/hr (18cm supernatant water depth) (.112 meters/hr) 37.9 L/hr (22cm supernatant water depth) (.154 meters/hr) 2012-08-09
31.101 L/hr (18cm supernatant water depth) (.116 meters/hr) 28.4 L/hr (22cm supernatant water depth) (.1158 meters/hr) 2012-09-27
28 L/hr (18cm supernatant water depth) (.105 meters/hr)
first day of temps below 4° C (40° F) at night this season
29 L/hr (22cm supernatant water depth) (.118 meters/hr)
first day of temps below 4° C at night this season
2012-10-03
40 L/hr (18cm supernatant water depth) (.149 meters/hr) 3.7 L/hr (22cm supernatant water depth) (.015 meters/hr) first flush diverter malfunction; turbid water clogged filter 2013-04-30
92 L/hr (18cm supernatant water depth) (.345 meters/hr) sand changed. .30 mm effective size. May 2013 24 L/hr (22cm supernatant water depth) (.099 meters/hr) sand changed, .25 mm effective size. May 2013 2013-08-27
75 L/hr (18cm supernatant water depth) (.280 meters/hr) sand changed. .30 mm effective size. May 2013 13.35 L/hr (22cm supernatant water depth) (.054 meters/hr) sand changed, .25 mm effective size. May 2013 2014-03-13
*Filter 4 and 5 are the newest filters.
Notes:
2009:
*Filter 2 and Filter 1 stopped flowing for three days due to below 0° C. temperature. 2009-03-11. All filters were restarted at the beginning of 2009, as they were frozen and the biolayer in each was destroyed.
**The supernatant water depth was increased in filter 3 due to a change in the float valve setting after the measurement taken 2009-04-08.
**48 L/hr at 18.5 cm actually represents a decrease in flow rate of L/hr per cm of water depth.
*** The temperatures have ranged from -2° C (28°F) during the day to -11°C (12°F) at night. The below freezing weather actually started (2009-12-04) but the filters continued to flow until 2009-12-07.

2010 (including POND FILTER):
As of November 23 2010, All filters - filter 1,2,3 and the pond filter are frozen and have ceased operation. Some damage is expected. The temperature is at minus 9.5 degrees Centigrade night (15° F) and minus 5.5 degrees Centigrade day (22° F) with 7.6 cm (3 inches) of snow on the ground.
As of December 8 2010, All filters - filter 1, 2,3 and the pond filter are back on line and operating. The pond filter stayed inoperative the longest. Possibly because the output pipe runs right through the frozen water on the inside of the filter thus making it take longer to thaw out.

2011:
As of Jan 5 2011,Filter 1 and the pond filter are frozen and have not been running for 8 days. The temperature at night has been minus 8 degrees Centigrade (17° F) and during the day 0 degrees Centigrade (32° F). Additional snowfall was 10 cm ( about 4 inches) as of December 28. Filter 2 and filter 3 are still running with water from the shallow well continuing to flow and filling the cistern which also has not frozen.
As of Feb. 06 2011 the pond filter is flowing at 144 l/hr. which is .553 meters per hour. (the sand surface area is .2600 sq meters. This flow rate is probably just slightly too high for good purification, so the water will not be ok for consumption (see link below).
As of March 8, 2011 the pond filter is flowing at 128 l/hr. which is .492 meters per hour.
As of April 16, 2011 the pond filter is flowing at 138 l/hr. which is .530 meters per hour.
July, 2011The filters 1,2,and 3 were inactive for 5 days in the first of July

2012:
Filter 1 was frozen and inactive for 1 week starting Jan. 15. There was a massive snow storm / ice storm here - many trees down and the power was out for 2 days. 14 inches of snow with a 1/8 inch coating of ice was the total. A state of emergency was declared by Governor Christine Gregoire. Filter 2 and 3 did not freeze and kept operating throughout the entire time. Temperatures averaged 25 degrees F for 5 days. All filters are now operating as of Jan. 24, 2012. Both pond filters were frozen for 4 days.

Originally, flow measurements were taken by recording the number of minutes required to fill a 12 litre container.
Most recently (2010-12-19) we are using a 4 litre container, as it is more indicative of instantaneous flow volume when measuring the flow from
a filter that is not fed by a steady flow of water. The 4 litre container was tested against the 12 liter container using filter 2 which has a steady flow (its input is controlled by a float valve and pressurized water). The 4 litre container was found to result in flow measurement precision and accuracy equal to the 12 litre container when the flow volume totals were averaged.
1 cubic meter = 1000 litres   1 litre = .001 cubic meter

We use flow rate per unit area per unit of time because we are interested in quantifying how fast the water flows past a given level in a given area. Simply measuring liters per hour does not give the full story. For example; 20 liters per hour from a 25 cm diameter container does not allow the same sand particle contact time as 20 liters per hour from a 75 cm diameter container, and sand particle contact time is critical for allowing maximum purification.
flow rate should be between .1 and .4 meters per hour (ideally between .1 and .3 meters per hour for the best results

This is how to figure the flow rate by just measuring how many litres flow per hour:
flow rate in meters per 1 hour = [(liters per 1hr)÷1000]÷(area of sand bed surface in square meters)


Explanation:
Here we will use X to mean multiply; and / to mean "per" as in per hour; and the ÷ to mean divide
L means litres and m means meters

In this formula, a cubic meter is represented by meters cubed or just: m3
(in other words meters X meters X meters or think of length X width X height the way we find volume)
And the area of the sand surface is represented by meters squared or just m2
meters X meters (length X width the way we find area)
Now, know that 1 cubic meter = 1000 Litres, or more simply: m3 = 1000L
Divide litres by 1000 to get cubic meters; or multiply litres by .001 to get cubic meters
If m3 = 1000L, then cubic meters/hour = Litres/hour ÷1000
(the per hour thing is there because we need to have a concept of motion over a time period
since it is 1 hour it does not change the result division by 1 or multiplication by 1 is identity)
or more simply: m3 per hour = (L per hour)÷1000
Now; m/hr = [(L/1hr)÷1000]÷m2
or just m/1hr = (m3/1hr)÷m2 (the m3 and m2 cancel out into just m so we end up with m/1hr)
Now, the above translated into language:
flow rate in meters per hour = volume in cubic meters per hour ÷ sand surface area in square meters
and finally back to where we started:
flow rate in meters per 1 hour = [(liters per 1hr)÷1000]÷(area of sand bed surface in square meters)

A simplified version of the above is:

For the shorter large barrel with a sand surface area of .26791 sq meters (23 inch diameter):
flow rate in meters per 1 hour = (53.75) ÷ (time in seconds to fill a 4 litre container)

For the taller smaller diameter barrel with a sand surface area of .2452 sq meters (22 inch diameter):
flow rate in meters per 1 hour = (58.73) ÷ (time in seconds to fill a 4 litre container)






HYDROCARBONS (TPH) IN ROOFWATER ARE SIGNIFICANTLY REDUCED BY A SLOW SAND FILTER SYSTEM
The most recent tests on fiter 1 show that a slow sand filter system of this design is capable of significantly reducing TPH (Total Petroleum Hydrocarbon) contamination in the water that passes through it. In this case the pre-filter system contamination is 2.9 milligrams per liter in the winter from water directly off of the roof. When we are talking about clean water, this is an unacceptable level for use as a water source without proper filtering. The slow sand filter system described here, which is in use with filter 1, has been in operation for 2 years without changing or cleaning the filter media. This system reduces these petroleum hydrocarbons from the roofing material (heavy oils), and (possibly) from air pollution (Diesel), down to less than one tenth of a milligram per 1 liter of water each (2 tenths of a miligram total); and this is when the filter is LEAST effective at 32 degrees F. This exceeds the MTCA Method A cleanup level for TPH in ground water as per the Washington State Department of Ecology 54 (page 4) by a factor of 10. The tests also show that petroleum hydrocarbons are removed by the first flush diverter to a level of less than 1 part per million (this exceeds the MTCA Method A requirement for groundwater which is 1mg/L). Also we know from the tests that over 40 percent of the hydrocarbons are Diesel. We do not know exactly how much hydrocarbon comes from local air pollution, which is significant in this area. The test for how much is due to the roofing material and how much is due to air pollution will have to wait. Funding is limited, and these tests are extremely expensive. The US EPA considers petroleum hydrocarbons (oil and grease) one of 46 other "non-priority pollutants" 55. There are not any "official" specific regulations for levels of TPH contamination in water set by the EPA. One of the reasons is that there are hundreds of compounds in petroleum and it is extremely difficult to identify each one and the effects each has on living organisms . We do know that there are between 5 and 10 million metric tons of oil entering the marine environment every year (as of 1986), and that oil spills are lethal to most forms of life. In spite of that, the EPA has yet to establish strict guidelines for TPH in water; and the studies they have done fail to show toxicity to humans. However, concentrations of some individual elements in TPH pollution above .001 mg/L have been shown to be harmful to aquatic life. 56 (p 203-206), 57 (p 220)

In addition to removing TPH contamination, Filter 1 removes coliform bacteria from 30,000 cfu per 100 ml down to 10 cfu per 100 ml (log credit of 3.477).This exceeds the Washington state Class AA (extraordinary) surface water requirements for the absence of coliform by a factor of 5, and this is when it is operating at minimum efficiency in 32 degree (Fahrenheit) weather.

Update, 2014-06-15:Filter 1, 2, 3, 4, and 5 are still running and producing clean water. More tests will be done as time and finance permits. Filter 1 has not had the sand changed for 6 years; and has only been wet-harrowed (cleaned) once in that time. The flow rate on filter 1 has stabilized to approximately 12 liters per hour overall average. There are now three 5 gallon slow sand filters running here. They have been in operation since September of 2013. There are also 3 pond filters in operation here. All of the filters, including the experimental 5 gallon filters improve the quality of water that runs through them. Filter 1 is the best so far. The 5 gallon filters are the least effective, but they do work marginally.
2011-01-13:The pond water filter test shows fecal coliform at less than 2 MPN per 100 ml.(less than 2 organisms per 100 ml of water. MPN means Most Probable Number) see this website for a good expanation of "MPN" per 100ml Not bad considering birds, squirrels, and other wildlife use the pond daily.
Build a Cistern and store water for the summer!
or Use a slow sand filter to keep a pond or fountain clean
NEW A summary of roofwater harvesting procedures

2010-01-05 Tests to determine total petroleum hydrocarbon pollutants in roof water from a composition roof are now available 2010-01-05: Total Petroleum Hydrocarbons (heavy oils and Diesel together) are significantly reduced by the slow sand filter down to less than 2 parts per ten million. Read the details below:   See a YouTube video of the roof water filter here

2010-05-18 Tests on filter 2 and 3 to determine total organic carbon content and on filter 1 to determine Snohomish county water quality standards compliance and total organic carbon content have gone in. The results will be posted when received.
2010-06-15: The filters passed all the tests by comfortable margins. The TOC was a little on the high side, but still acceptable, and was much better in filter 2 and 3 actually being reduced.



1. The first filter (filter 1   2007-08-13) configuration was put together with very casual attention to detail and operated with only "human" power (10 gallons of water was added manually each day). This was done deliberately to verify the validity of this question: Can a working biological sand filter be put together with mostly recycled material at very low cost (under 25 dollars) using construction grade sand and average skills? The answer - partially. The test results showed no fecal coliform bacteria from stagnant roof water runoff but some coliform present. This water would be ok for everything except consumption and better than water straight from a "rain barrel".

2. The second configuration of filter 1   2007-10-09 was the addition of graded sand (.15 mm effective size) to the top layer of this filter and ungraded "fine" sand to the bottom layer. These were the only changes to the filter detail. This filter removed 99.9 percent of all coliform bacteria (including ecoli and fecal coliform) and removed more of the color from the roof water runoff - still not ok for drinking on a regular basis but 99.9 percent better than the rain barrel water and much safer. With only close attention to the detail of the size of the top layer of sand, the filter is now functional.

3.The third configuration of filter 1   2008-02-12 was the addition of a first flush diverter to the system. This allowed for significant improvement of turbidity (as determined by visual inspection) and some reduction of the bacteria (as determined by laboratory tests) before the water was put into the filter. Still the same result - removal of 99.9 percent of all coliform bacteria.

4. The fourth configuration of filter 1   2008-02-12 involved the addtion of a small dc powered pump to recirculate the water through the filter. This was an attempt to keep the biofilm alive without having to manually add water each day. The dc pump is operated with a very small amount of power and can be run by a solar panel. This worked. The filter still removed 99.9 percent of all coliform. As of 2008/12/01, this configuration of Filter 1 has been in continuous operation for 14 months without disturbing the biolayer (schmutzdecke). The flow rate is 3 liters per hour as of 2008/12/01. The reason for this long undisturbed run is to determine if a slow sand filter becomes more efficient at removing contaminants as it ages. The compromise would be in flow rate: significantly reduced flow rate to obtain significantly increased water quality. This filter uses water from a composition roof as its source. This water should contain unacceptable amounts of hydrocarbons from the roof surface. The question is: will the aged slow sand filter remove enough chemicals and pathogens to produce potable water?   Update 12/18/2008: Two samples of water were taken from this filtering system (the fourth configuration of filter 1) just before the freezing weather hit: Filtered water and unfiltered water. The filtered water had been through the slow sand filter and the unfiltered water was taken from the storage container that provides the raw water source for the filter.(filter 1) The samples were put into two separate containers which were identical and were cleaned and sterilized. These containers were put in a building where the temperature was 32 degrees F. The filtered water froze and the unfiltered water did not freeze. It is a known scientific fact that water containing dissolved substances freezes at a lower temperature than water with less dissolved substances. (this is why salt is put on roads to "thaw" out the ice - the salt slowly lowers the freezing point of the ice and causes it to "melt".) Since the filtered water froze and the unfiltered water did not freeze (the surrounding temperature was not low enough to freeze the unfiltered water - it's freezing point was lower than the filtered water - for some unknown reason), did the filter remove dissolved chemicals? A test will go in as soon as money, time and weather permit.

5. Filter 2   2008-05-24 is 12 inches deeper than filter 1 with more graded sand (.15mm effective size), and the water input is from a shallow well. This filter uses the dc pump modification and is fully functional - it removes 99.9 percent of all coliform bacteria and the water has no roof chemicals in it. This is potable water with one (albeit only slight) caveat: chemicals or pollutants present in the sand will be in the output water. This condition can be checked with a thorough water quality test, if no poisons are found in the water then it is potable and probably the best water around.

6.Filter 3 2008-10-09 is now in the process of becoming fully operational. This filter contains all NSF/ANSI 61 - AWWA 100 approved (the two standards for potable water) sand. This means we know there are not poison chemicals in the sand. The top layer of sand is .25 mm effective size and the bottom layer is .35 effective size, however these sands have known uniformity coefficients of less than 2. The container and all the pipe are also ok for potable water. A test will be done on the water in about 3 weeks. (3 weeks from Sept 19 2008). As of Sept 23 the flow rate is 38 liters per hour (approximately 10 gallons per hour.)
2008/11/07 Update: An excessive amount of alge has formed on top of the sand in this filter. This has drastically slowed down the flow rate - from 10 gallons per hour to 3.6 gallons per hour. It only took 4 weeks for this algae to build up. The cleaning process, however is very simple. This is a description of what was done ( it is called "wet harrowing"):
I removed the top of the filter and GENTLY ran my hand over the top 1/4 to 1/2 cm of sand until all the surface of the sand had been agitated. The water became cloudy with fragments of algae. This part of the water was drained off. There was an almost immediate change in the flow rate, although I would recommend plugging the output while the filter is being cleaned. I installed a drain pipe on the top of the filter so water can be run through the input baffle pipes while the excess cloudy water is drained off. When the water draining off became reasonably clear, the top cleaning drainpipe was closed and the filter was allowed to resume operation. The flow rate measured 48 hours after this procedure was 28.965 litres per hour (7.65 gallons per hour). The biolayer must have time to re-grow however, so the water will not be safe for several weeks.

7.2009/02/17: Added a float valve to filter 3.


2008/11/10 Update: The test that went in 2008/10/29 has come back on filter 3. All coliform bacteria are removed by the filter.
2008/12/18 Update: Due to extremely cold weather (for this location) all the filters have completely frozen and stopped operation. The temperature has been below freezing since 2008/12/12

2008/12/27 Update: New information from the results of research regarding the viability of composition roofing material for water collection are posted on the FAQ page.

2009/01/16 Update: The filters are now running again. The below freezing weather lasted until the first few days in January 2009. In this location, temperatures were below 20 degrees for nearly one week, and dropped to below 15 degrees F for several days. There was 16 inches of snow on the ground. All the filters were inactive and frozen for 3 weeks. Pipes were cracked and brass valves were destroyed. All the pipes were wrapped with insulation, but that did not help because the water inside the filters froze. In climates where below freezing temperatures occur, these filters MUST be kept from freezing.

2009/01/26 Update: The filters have frozen again. There was an inch and a half of snow last night. Below freezing weather finally froze all the filters as of today. Operation has been sporadic for the past nine days - night temps have been near or below 32 deg F. .

2009/02/08 Update: Both filter 2 and filter 3 were damaged because of the cold weather. They have been disassembled checked and put back together. This meant carefully removing all the sand and gravel from each filter cleaning the container, replacing cracked drain pipes and putting the sand back in. Each filter contains approximately 900 lbs of sand and gravel. This is VERY labor intensive work. The re-assembled filters are now running. Filter 2 has been running since Feb 3 2009 and has a maximum flow rate of 72 litres per hour (19 gallons) with 20 cm (7.5 inches) of water covering the surface of the sand. Filter 3 has a maximum flow rate of 90 litres per hour (23 gallons) with 16.5 cm (6.5 in.) of water covering the surface of the sand and has been restarted again on Feb 13 2009.

2009/03/11 Update: All the filters except filter 3 with the float valve have stopped operation, are frozen and have been for 3 days ( this is the fourth day ). Record low temperatures here were below 19 degrees F. and there has been a total of 5 inches of snow at this location in the past week.

2009/03/13 Update: All the filters are now back in operation.

2009/04/07 Update: Filter 3 flow rate: .75 litres per minute (45 litres per hour) with 16.5 cm water depth over the top of the sand. (11.89 gallons per hour)
Filter 2 flow rate: .71 litres per minute (42 litres per hour) with 16.5 cm water depth over the top of the sand. (11.25 gallons per hour)

2009/12/08 Update: All filters are frozen. The temperature has been below freezing for five days, and below 18 degrees F the past two nights.

2009/12/22 Update: All filters are now in operation.

2009/12/27 Update Temperatures the past 4 days have been below freezing at night (25 degrees F), however the water in the filters has not frozen.

2011/01/03 Update The pond filter output water went in for a Coliform test, and a turbidity test December 27th. We expect results back within the next two weeks.

2012/01/16 Update The pond filters have frozen as of Jan 16. Filter 1 and the newest, Filter 4, have also frozen as of Jan 16. Snow total so far for this storm is 9 inches at this location. Filter 2 and 3 are still in operation.

Clean water is necessary for life, without it people cannot live. As the population of any given area increases the demand for clean water increases. At the same time more water becomes unsuitable for human consumption. Aquatic life, including many species of fish that support human life also suffer. To prevent human suffering and conflict, clean water must be freely available to all people. In most areas of the world today clean water is not freely available to anyone. In fact, in most parts of the world clean water is available only for those who can afford it. Polluted water is the only option for billions of people. This must change. Clean water must be freely and unconditionally available to all people. If it is not, there will be dire consequences that will make our current warfare over petroleum resources seem insignificant. The solution to water availability lies not in expensive corporate distribution systems, but in individual or small scale water filtration systems, and the knowledge of how to build and safely maintain these environmentally sustainable systems to provide uncontaminated water.
note 1:   Water can be contaminated by many different things: inorganic chemicals, organic chemicals and compounds; and many different types of viruses and bacterium and it is impossible to test for all of these contaminants without access to expensive elaborate testing facilities. This website and this study must not be interpreted as a cure-all for the ills of water supply problems. The water that goes through these filters is NOT being consumed, and they are NOT part of the plumbing in the dwelling unit nearby; and furthermore, consuming water that goes through any filter is NOT RECOMMENDED without full knowledge of the source of the water and EXACTLY what may or may not be in the source water; and a complete EPA approved test on the water before and after any filtering system used to determine the safety of the water. That said, it must be recognized that even public water supply systems are subject to contamination, 22 40,41 although these systems are continuously monitored for harmful substances by highly qualified technicians. Biological sand (slow sand) filtering is not used in most public water supply systems. Slow sand filters are very efficient at purifying water (they actually remove pathogens) and they are the best and most efficient way of removing cryptosporidum cysts from water without adding chemical poisons. Most public water supply systems in the U.S. do NOT use slow sand filters, they use Chorine or Ozone combined with highly complex mechanical filtration systems to remove particulate matter and inactivate and / or remove pathogens. However, chlorine and Ozone react with organic matter in water and produce cancer causing substances: trihalomethanes (from chlorine), halacetic acid (also known as Acetic acid, dichloro; bichloracetic acid; DCA; dichlorethanoic acid; 2,2-dichloroacetic acid; dichloroethanoic acid; kyselina dichloroctova or Urner's liquid) (also from chlorine) 51 and formaldehyde and ketones (from ozone)23, 24 that are still in the water (at low concentrations) when it arrives at the consumer's plumbing and are VERY harmful if consumed over long periods of time even at low concentrations. Bromide (present in ground water) and chlorine added to kill bacteria plus sunlight equal bromate - a cancer causing chemical. This situation occurred in 2007 in Los Angeles. The Sliver Lake and Elysian Reservoirs had to be drained, refilled and black plastic balls put on top of the water to keep sunlight out.42

note 2   Why is this "good" news? I wasn't going to get political here, but this is so important and teaching is, after all, a political act (Paulo Freire) . . . . Four reasons stand out:

One; Enough water for survival should be free for everyone. It is as necessary for life as air - that one is sort of a no brainer.

Two; If enough people in the city catch rainwater in rain barrels, the load on the storm drains is reduced considerably - and there is less chance of the drains overflowing and spreading contaminated water into the environment before it is treated. This is good news for everyone, as less pollution is washed into streams, rivers, lakes, and oceans during a significant rain event.

Three; In the summer, water can then be conserved by using the stored water for flower gardens, lawns, and if filtered by a slow sand filter, vegetable gardens; thereby significantly reducing the load on the public water supply.

Four (and probably the most important); It appears as though government is finally getting a clue. . . hopefully I'm not wrong about this. Good job Wa. state gov., thank you! Tax dollars well spent this time!



And, speaking of political stuff, who is funding this site, and why is it on the internet? There are no multinational corporations, environmental groups, universities, or political groups involved in the funding of this site. The funding is private, unconditional, and limited to maintaining the domain name and hosting, paying for the epa certified tests; and purchasing parts used to build the filters. If any outside funding, or donations are offered, the conditions will not change - the funding must be unconditional. The website coding, physical work and research are done without any monetary compensation. Every effort is made to assure that unbiased results based on factual evidence and professional testing are presented. Hazards are noted. No guarantees are offered or implied. The creation, maintenance, and content of this site have no connection to any political group. Additionally, this website has no connection whatsoever to any religious group. This site is here because it may be helpful to others.

IMPORTANT: Most raccoons carry a type of parasitic roundworm called Baylisascaris procyonis 43, 44, 45, 46, that causes very serious illness in people. If there are raccoons in your area be aware that your yard may be contaminated. Children are highly at risk. DO NOT use water from a rain barrel, pond or creek unless you are absolutely certain that it is not contaminated. Read the literature cited from the link above (43, 44, ,45) on this issue completely. You have been warned.

Before any water from a non-public utilty monitored slow sand filter is used for drinking on a regular basis, it is HIGHLY recommended that a UV filter be installed permanently in the water line to the point of use, and approval from your local health authority be confirmed. Note that none of the filters described on this website are being used to supply potable water. The water from these filters is NOT being used as drinking water, and furthermore, the operation of any filter is totally the responsibility of the owner/operator. Know that ANYTHING CAN BE IN WATER, and water quality will vary considerably depending on the surroundings. Note: In the past seven or eight months websites describing biological sand filters / slow sand filters have been appearing with instructions recommending BACKWASHING a biological sand filter when the flow rate slows down. Forcefully backwashing a slow sand filter, particularly a small slow sand filter with layers of different sizes of sand, will destroy it. The flow rate is slowed by a buildup of material on the TOP FEW CENTIMETERS of sand. Simply gently agitating this layer and DRAINING OFF the cloudy water is all that needs to be done. These well meaning people have apparently confused rapid sand filtration with biological sand filtration. There are small scale biological sand filters that have been carefully engineered to allow reverse flow of water to clean the filter, but the sand bed is not "fluidized" as it is in the process of "backwashing". 52

back to top   back to faq page   back to faq 31

Page design by Perpetual PC's
Creative Commons License
This work is licensed under a Creative Commons Attribution Share Alike 3.0. terms of use              Valid XHTML 1.0 Transitional