Rainwater Filtering

Rainwater filtering is done in stages. The cleaner the water going into your storage tank, the less often you will need to drain and clean the tank. Rain water coming off a roof will inevitably contain dust, leaves, sticks, bird dropping and other debris.

The first stage is a gutter shield of some kind. There are many companies that have products that cover the gutters and stop the leaves and twigs from trees from filling up the gutters around your catchment area.

The second stage is what is called a First-Flush. The "first flush" of rainwater is sacrificed to make the rest of the water cleaner. The diverter routes the first flow of water from the catchment surface away from the storage tank.

Each downspout should have first-flush diverter. It can direct the water to a plugged pipe that looks much like the typical downspout, except it has a sewer clean out plug at the bottom.

With the plug in, the water fills the downspout until it reaches the top. From here, the water is directed down to the collection pipe, which goes into the tank. Each of these first-flush filters should be drained of debris after each rain to be ready for the next rain event.

While leaf screens remove the larger debris, such as leaves, twigs, and blooms that fall on the roof, the first-flush diverter gives the system a chance to rid itself of the smaller contaminants, such as dust, pollen, or bird and rodent droppings.

One rule of thumb for first-flush diverter is to divert a minimum of 10 gallons for every 1,000 square feet of collection surface.

Another option would be a roof washer. The roof washer, placed just ahead of the storage tank, filters small debris for potable systems and also for systems using drip irrigation.

The box roof washer is a commercially available component consisting of a fiberglass box with one or two 30-micron canister filters (handling rainwater from 1,500- to 3,500-square-foot catchments.)

From either the first-flush diverters or a roof washer the water then goes to the tank or cistern.

At this point the water can be used for non potable uses such as watering the lawn or gardens, or something like flushing the toilet.

It is not filtered or purified enough yet for human consumption yet. The third step in rainwater filtering will produce water that can be used for drinking, cooking, etc.

Several treatment options, including micro filtration, UV purification or ozonation are available. Most experts agree that filtration and UV treatment will provide adequate protection.

Most systems use a combination of physical filters, which remove particulates, and a UV-light chamber, which kills bacteria and other organisms by exposing them to high-energy ultraviolet light.

Rainwater filtering should include a commercial five micron or less fiber cartridge filter followed by a three micron or less activated charcoal filter. The fiber filter will remove particulates and the carbon filter will remove very fine particles and improve taste. Filter elements should be replaced according to the manufacturer’s instructions.

After physical filtering, the water must be disinfected by either chemical injection, ozone generators, or by a UV light. Most people prefer the UV light because it does not leave chemical residuals in the water.
UV light systems should be listed to the ANSI/NSF 55 standard for Class A UV water treatment systems.

Remember that although the water is considered safe to drink following this treatment, it should never be connected with another drinking water supply without a reduced-pressure principle back flow preventer.

In fact no municipality will allow a direct connection. Back flow devices are required to be installed.

You know have drinking water for your family that is nearly free and is good quality water.




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