Design roof, gutters and first flush for drinking-quality rainwater
The roof is the first stage of your treatment train. The right materials and a first flush diverter keep most dirt, droppings and metals out of the tank.
How
- Choose roofing suitable for potable collection. The Texas manual recommends plain galvanised metal or metal with epoxy or latex paint; it advises against asphalt or composite shingles because toxins can leach, and limits wood, tar and gravel roofs to irrigation.
- Avoid lead. Australian enHealth guidance says drinking water catchments should not include uncoated lead flashing, and warns against lead-based paint, exposed treated timber and bitumen roofs. The Texas manual says no lead solder in potable gutters.
- Slope gutters toward the downspouts and size them for intense rain. Long or steep roof planes and valleys can overshoot gutters, so ask a gutter supplier.
- Fit leaf screens and keep branches away from the roof, as enHealth advises, so birds and animals have less access.
- Fit a first flush diverter sized to the roof. The Texas manual gives a common rule of about 10 US gallons per 1,000 sq ft (about 0.4 L per square metre); enHealth suggests 20 to 25 L per rain event for an average roof. Make sure it empties between storms.
- Make the tank inlet easy to disconnect, so you can divert water during smoke, ash or roof work (enHealth).
Safety: Working on roofs is a fall risk. Use proper ladders, harnesses or a roofer.
Do these first
Sources
- The Texas Manual on Rainwater Harvesting, 3rd edition. Texas Water Development Board, accessed 2026-11
- Collecting Rainwater and Your Health: An Overview. US Centers for Disease Control and Prevention (CDC), accessed 2026-11
- enHealth Guidance on the use of rainwater tanks. enHealth, Australian Government, accessed 2026-11