Rainwater

Rainwater for non-potable uses: how to plan the system

Collected rainwater can serve non-potable uses when the system is designed for that purpose. Learn how to separate networks and plan treatment and maintenance.

LJS Soluções AmbientaisPublished on September 23, 2026

Rainwater collected by a gutter and filter flows to a closed cistern with a separate irrigation outlet

In brief

Define the intended use and required water quality first.
Roof, gutters, first flush, filter, storage, and distribution form one system.
Clear appearance does not prove water is potable.
Identify and separate non-potable plumbing from drinking-water plumbing.

Stored rainwater can reduce demand on other sources for compatible uses such as irrigation or floor washing. Safety depends on intended use, quality, collection, and maintenance. Water should not be considered safe to drink because it looks clear.

Define the use before selecting components

List outlets, estimated demand, seasonality, and the impact of interruption. Irrigation, washing, and toilet flushing have different needs; other uses may need specific assessment. Treatment must suit the use, materials, and local requirements.

Water for drinking, food preparation, or personal hygiene must meet applicable drinking-water requirements. Brazil's Ministry of Health Ordinance 888/2021 does not allow potability to be assumed without meeting those requirements.

Plan the water path

Roofs and gutters can collect dust, leaves, and contaminants. Assess roofing, screens, first-flush diversion, filtration, tank inlet, overflow, and cleaning access. A closed tank limits light, debris, and animal entry. Label pipes and outlets so they are not confused with the potable network.

Prevent cross-connections

Keep networks independent and prevent rainwater from flowing back into the public supply or mixing with drinking water. Backup supply must preserve hydraulic separation under the design and applicable rules.

Inspect and maintain

Include gutters, screens, first-flush devices, filters, covers, overflow, pumps, pipes, and outlets in the routine. Inspect after dry periods, heavy rain, or roof maintenance. For sensitive uses, define water-quality parameters, sampling, and treatment with a qualified professional.

References

Sources checked 23 September 2026. This article covers non-potable uses and does not replace public-health assessment or local requirements.