This is a summary in outline form of the last four posts:
Critical considerations when setting up a small slow sand water filter:
A. Sand size
.35 mm effective size is the best overall choice
B. Input water turbidity
Turbidity levels below 5 NTU are best.
C. Constant water flow must be available
Water must flow through a biological sand filter (slow sand filter) constantly.
They cannot be allowed to sit idle, and the water must come from the same
source all the time. Some sort of recirculation of already filtered water must
be provided during dry spells when rainwater is being filtered
D. Container must not be smooth on the inside
The inside of a plastic container must be rough and not smooth. #60 grit
sandpaper can be used to score the inside of the container horizontally.
If the inside is smooth, contaminated water will slip down the sides
between the sand and the plastic.
E. A first flow diverter may be necessary
A first flow diverter (often callled a first flush diverter) must be used in
most cases, unless the roof surface is completely in the open and there
is minimum air pollution surrounding the area.
F. Stop output flow when wet-harrowing
When wet harrowing the filter, the output must be completely shut off
before the procedure starts.
G. Pre-filtering of roof water runoff is absolutely necessary in most situations
Some sort of prefiltering of roof water is necessary, such as a first flow
diverter, a roughting filter, screens on the gutters, or inserted into the
If the above recommendations are not followed, failure is highly likely.