Being an engineer, I just couldn’t bring myself to accept that the classic roof washer concept was the BEST way to insure that only clean rainwater gets into the storage tank… The usual first flush roofwasher idea is to collect some predetermined number of gallons from the beginning of the gutter flow (which contains the largest amount of roof litter and contaminants) and then let the remaining water flow past the roofwasher into the tank. The fact that such a system must deal with pollen in the spring, bugs in the summer, leaves in the fall, ice in the winter and relies so heavily on vigilant maintenance all year long seems to spell trouble. Not that roofwashers are a BAD idea – they are probably the best filtering system you can build with parts from the average hardware store – but there just had to be a more reliable way.

I think I found it. Germany has standards that home rainwater harvesting systems must meet, and the key feature of these standards seems to be that the systems must be foolproof enough to work for homeowners who aren’t rainwater collecting enthusiasts, who aren’t dedicated maintenance men, and who probably don’t really even know how their rainwater system works. This goal of simplicity and ruggedness is something the rest of the world will need to adopt for RWH to become successful and commonplace.

I’ve found info on three approved German RWH systems so far and the heart of each system is a self-cleaning filter that replaces the usual roofwasher. These self-cleaning filters are simple designs that incorporate some fine engineering (the best design combination in my experience). They will not plug up with big debris and even if you never do the yearly filter cleaning the worst that will happen is that all your rainwater goes down the wastepipe and your storage tank becomes empty.

The best of the bunch seems to be made by WISY. It has the added benefit of a very fine stainless steel screen that must become “wetted” before it starts to pass water through. This is a benefit because it means the first flow of rainwater collected will flow over the initially dry screen and out the wastepipe – like a roofwasher. And after that you get fine filtration of the rainwater while the wet sticky gunk gets rinsed down the waste pipe.

Have any of you had experience with these self-cleaning filters? Are they as good as they look? I’m ready to spend some hard earned money on one to build my system around and it sure would be great to hear your thoughts.

I don’t have personal experience with the WISY filter, but I *was* able to see it in action at the Renewable Energy Roundup in Fredericksburg, TX, last fall. The US distributor had a working display and also did a session. Looked impressive. I’ve already decided that if/when we collect rainwater at our new house, well use the WISY filter system.

I saw a demo at the Renewable Roundup in Fredericksburg Texas about 4 years ago. I was really impressed as well. In our case we have a home business hence we are here almost all of the time. Our area usually gets rain in equal amounts every month throughout the year. Because of those two factors we built and use a complete manual system: when it rains I wait a while and then screw in a 4″ cap. Because of the way our house is built we have four downspouts. Often our rain is torrential so we really can’t T the downpipes together. Putting up four of these monsters would be especially painful. I’d be real interested to have one in hand to see how difficult it would be to build one out of readily available parts. Can’t do it from memory as the last time I saw one was over 4 years ago. The mind is the second thing to go.

If it is of any interest, on my rainwater system, I first used a coffee filter, the permanent kind (without any roof prefilter)… but the pressure on a rain downpour pushed holes through the coffee filter, so that it wasn’t good anymore… then I resorted to plan B… which was to use a piece of fiberglass screen wire… this did work good, but it did not catch the fine particles of dirt… I did find a piece of fine stainless steel screening, to illustrate the size of the filter holes, it was similar to the screen in a faucet aeriator… and this did work good too… I also have a home made sand filter which will really clean the water before it flows into the final household tank.