Roof rainwater catchment: Gutters, first flush and cisterns · Alt Ordo Systems Guide
A roof is a free water collector. Gutters gather what falls on it, a first-flush diverter throws away the dirtiest first gallons, and a covered tank stores the rest for dry weeks. A clean system gives you garden, washing and livestock water with no pump at all. With filtration and disinfection it can be your drinking water. The real design work is sizing the tank for your dry season, and keeping the water clean from the roof to the tap.
This guide helps you work out how much rain your roof can give you and how much tank you need for the dry season, then build a clean catchment from gutter to tap: leaf screens, a first-flush diverter, a calmed inlet, a guarded overflow and a floating outlet.
What's inside. 25 pages in 9 chapters (At a glance, Where it works, How it works, Size it, Parts and cost, Build it, Run it, Rules and permits, How it connects), then the sources and a notes page. 12 numbered figures drawn for this guide, including a fit map of every US county. You also get a worked example with a fill-in worksheet, 12 numbered steps, a year-round calendar, and a troubleshooting table.
Three builds, costed line by line (typical US prices, October 2026):
- Bare-bones: $780–$1,440
- Standard: $2,040–$2,650
- Comfortable: $4,810–$5,980
Sourced and fact-checked. Facts and figures are cited to the 17 sources listed at the back, and the whole guide was fact-checked before release. General guidance, not engineering advice: your county and a qualified pro have the last word on your site.
Pairs with other Alt Ordo Systems Guides: Safe drinking water; Off-grid solar; Wells and hand pumps; The off-grid vegetable garden. For your county's permits and rules, see our county and state guides.
Instant PDF download. After checkout you get a download link by email. Letter-size pages, made to read on screen or print at home.