Tag Archives: potable

Rainwater Catchment, Residential Rainwater Collection

Can I Collect Drinking Water From My Roof in Seattle?

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Seattle skyline featuring the Space Needle under a cloudy sky.Does Seattle allow rainwater collected from the roof to be used for drinking water?

You can have a potable rainwater collection system designed by an engineer, licensed in the state of Washington with experience in RWC, or an ARCSA(American Rainwater Catchment Systems Association) accredited professional. Knowledge and experience are required for potable design in King County. A properly designed filtration and disinfection system can provide quality drinking water. It is the designer and installer’s responsibility to ensure that an adequate system is in place and correctly installed.

After system install has been completed, it is up to the owner or operator to maintain the system to protect users from possible contaminants. Sampling and testing are essential to ensure the system is performing as designed. It is recommended that filtered, disinfected rainwater should be tested annually.

Mountain landscape with a clear blue sky and green forest.A typical filtration/ disinfection system consists of a sediment filter, activated carbon, and ultra violet light and is adequate for achieving potable standards. Adding a 1-micron absolute sediment filter before the UV adds a higher level of endurance of cyst removal. Other possible contaminants can be identified by testing “raw water” before the filtration train and then can be removed by additional filtration. The last device should be an ultra violet light, which must carry a “class A” rating.

Quality drinking water is possible with rainwater collection and is legal in many counties in Washington State, including Seattle. Many are finding the alternative appealing to municipal water supplies, while also helping to reduce stormwater runoff. Seattle Public Health encourages the practice of rainwater collection, as does Washington State Department of Ecology.

Rainwater Harvesting Education

Is Drinking Rainwater Bad for Us?


Refreshing lemon slices in sparkling water with bubbles.Although rainwater is generally considered clean, it can carry microbial and viral contamination generally caused by birds, rodents and insects. However, rainwater is relatively easy to filtrate and disinfect, resulting in improved quality overother drinking water supplies.

The Environmental Protection Agency (EPA) regulates the quality of public drinking water, but not private systems. The treatment of rainwater should be equal to that of surface water. All collected rainwater used for potable supply must be treated effectively to minimize risk of human health hazards. Contaminates need to be removed by filtration and sorption, or inactivated by disinfectant.

Both organic and inorganic contaminants need to be considered in design and installation of a rainwater collection system. Microbial and viral contamination in a rainwater collection system can be reduced by proper collection techniques such as screening, first flush devices, or vortex filters before storage. Environmental contaminants such as pesticides, fertilizers, and hydrocarbons should be considered, too. Raw water testing from the downspout at time of design will insure proper filtration in the treatment train, if needed.

Raw water should be tested to ensure that a RWC system is designed to produce high-quality potable water and tested after installation to be sure that the filtration and disinfection system is effectively removing any contaminants of concern.

To ensure that a RWC system is producing high-quality water, testing must be done. The EPA and local health agencies specify methods to analyze drinking water. Laboratories that conduct these tests are certified and governed by regulatory agencies. It is recommended that collected rainwater intendedfor single family domestic use be tested once per year for bacterial and any other constituents that are a concern.

Rainwater Catchment, Residential Rainwater Collection

Project Update: Two Sole Source Potable Rainwater Systems

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White truck crossing a narrow suspension bridge over a river.RainBank Rainwater Systems was contractedto install a 10,000 gallon, sole source, potable rainwater catchment system in Baring WA, just east of Index. The system was designed by Chris Webb, PE of Herrera Environmental Consultants for a single family dwelling. The system will provide potable whole house usage as the only source of water for this 839 square foot home. With 41.2″ annual rainfall, the system is capable of supplying 100% of the household demand based on occupant’s usage requirements.

The small parcel size and the small bridge over the Skykomish bridge limited the feasibility of safely drilling a well and there is no public or community water system. RainBank Rainwater Systems always enjoys a challenge – and this one has many – from a very small lot with wetlands, large boulders throughout the property, the bridge, and location of site

Two large black water storage tanks in a rural setting.RainBank Rainwater Systems hasrecently begunconstruction of another 10,000 gallon, sole source, potable rainwater collectionsystem in the Skagit River Basin, which has been affected by the in stream flow rates, along with a well drilling moratorium. The system was also designed by Chris Webb and Herrera Environmental Consultants for a single family dwelling. Again, the system will provide whole house potable water as the only source of water. The house is3500 square feet, so 33.2″ annual rainfall will meet the daily demand for 95% of the days in this model with no change in use. The reality is, that the occupants would decrease usage during times of drought and therefore the 2 – 5,000 gallon cistern volume is considered capable of supplying 100% of domestic use.