Water in glass
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
Please help support this site by purchasing, for seven dollars and fifty cents, a summary of the most important results of our research for the past 8 years, including detailed drawings of the filters, where to find sand, pictures, and an easy to understand faq of important considerations in the assembly of a small slow sand water filter. This page on our blog has the purchase area. Thank you!!

Slow sand filter float valve flow control device in filter 3 and filter 2
The pvc pipe is 1/2 inch. There are .040 inch holes drilled on the bottom of the pipes to allow the water to disperse without disturbing the sand surface.

The float valves limit the volume of the flow of input water so it matches the volume of the flow of water through the filter. As the filters "ripen"
their flow rate will slow down. The float valves will, by their nature of operation, slow the flow of water down equally.
The drawing below is of filter 3, the filter 2 drawing with the float valve installed is not yet done.
slow sand filter with float valve

float valve
This is the newest float valve installed in filter 2.
Note the "schmutzdecke" (dark color) on the white sand.
(This is not usually visable on all functioning filters)

float valve closeup
This is filter 3 with the float valve installed.

float valve external

float valve and hose

The "schmutzdecke" is not necessarily visible on all filters. Filter 2 has deliberately not been cleaned
specificaly for the purpose of illustration and testing so it is possible to see the accumulation of substance that
occurs over time. "Schmutzdecke" is just a fancy word for the top biolayer that does most of the work purifying the water.

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