Rainwater Catchment Systems - frequently asked questions
The FAQs below address some basic concerns you may have about installing a rainwater catchment system.
Yes! Washington State has ruled that water rights are not necessary for rooftop rainwater harvesting as long as it is used on site. See here (external link) for more information.
Your initial investment depends on how big of a project you undertake. Some factors to consider:
- How big is your catchment area (roof)?
- How big is your garden?
- How much will you be relying on irrigation rather than rain to water your plants?
- You may find this Calculator Tool (external link) useful in thinking about how big of a tank you need.
And remember, you may be eligible for financial and/or technical resources to help install a rainwater catchment system. Learn more about incentives throughout the Puget Sound region here (external link).
Most often gravity will provide enough water pressure for your garden hose. If you are having trouble, you can try elevating your barrel/cistern or moving it closer to your garden. If that still isn’t working, there are small inexpensive pumps and drip irrigation systems on the market which will get the job done.
In most residential systems, water harvested from rooftops is NOT safe to drink. There are steps you can take to make your water potable, but they require considerably more intricate and expensive systems. You can read more about various filtration and purification methods here (external link). Before installing a filtration system, be sure to check with the Public Health Department as they have strict standards on water for indoor use.
Credible research says yes (mostly). An interesting overview, including some easy steps you can take to stay on the safe side, was just created by Sightline Institute (external link).
Yes, around the world people use harvested rainwater for flushing their toilets as well as washing clothes, cars, floors, pets, or even themselves! Make sure you know what’s in your water before you use it for anything, as chemicals picked up from your roof or metal gutters can have unintended effects. Using a system that discards the first flush as well as having non-toxic roofing and gutter materials can help ensure water quality. If you plan to use your water for indoor purposes, you’ll need to check with the Public Health Department as special treatment is needed. Arid states with water shortages have more lenient regulations when it comes to allowing indoor use.
Yes, depending on where you live in King County.
- Green Stormwater Infrastructure Mini Grants (external link): available within the King County Wastewater Treatment Division service area
- RainScapes: available for unincorporated King County
- RainWise: available for some Seattle neighborhoods
- Other incentives throughout the region