The Problem Index → Water
I want to collect rainwater off my roof
A 1-inch rain on 1,000 sq ft of roof is about 623 gallons, which surprises most people. The one piece almost everyone skips is the cheapest and most valuable: a first-flush diverter.
What actually works
◆ Proven
The first-flush diverter
About $40 in PVC. Dumps the dirtiest water of every storm — the dust, droppings and grit — for under 2% of the yield.
$40 in PVC◇ Plausible
Check your state law
Rainwater harvesting is encouraged in most states and restricted in a few. Look it up before you plumb anything.
✕ Avoid
First flush is not treatment
Treating diverted roof water as drinkable is the dangerous mistake here. It still needs filtration and disinfection before anybody drinks it.
Run the numbers
- Rainwater catchment calculator → — free calculator, works offline.
- Water storage: how long it lasts → — free calculator, works offline.
Also searched as
rainwater harvesting · how much water from my roof · rain barrel · cistern sizing · gutter to tank · catchment system · is roof water safe