We are now approaching our 8th year of slow sand filter operation here. The first filter we started back in 2007, filter 1, is still running, and producing clean clear water. It filters rain water run off from a composition roof. It removes 99.99 percent of bacteria from the input water, and also removes petroleum contamination (see the 9th 10th reports down from the top at the link page shown) that is present in the water from contack with the roof surface, and air pollution.
The 5 gallon filters we tried last winter for the most part failed. The remaining two 5 gallon filters out of the 4 we started with, are running in series. We hope to test these in late February.
All of the pond filters are running, including the first one we put together four years ago.
There are two filters that have continued to run through two 20 degree (F) weather events which lasted 10 days each. They kept running because the input water is taken from a well that has a 100 watt incandescent light bulb heating the water before it goes into the filters. The water is kept running 24 hours a day at a very slow rate – about 20 to 30 gallons per hour. We have shown here, that it is possible to keep slow sand water filters outdoors and keep them running where there are not severe winters.