Rainwater
harvesting.
Tell us your roof area and what the water is for and we will size the bank for you — it is usually fewer totes than people fear or more than they expect.
Yield = roof area (sq ft) × rainfall (in) × 0.623 × 0.9. A 1,200 sq ft roof in a 1-inch storm gives about 673 gallons — two and a half 275 gallon totes from one ordinary rain. For irrigation, technical grade is correct and costs about 45 cents per gallon of storage. For anything potable, food grade or rebottled plus treatment, plus a permit.
Sizing, properly
The common mistake is sizing for the storm instead of the drought. The storm fills your tank in minutes; what matters is how long you need to go without rain. Work it backwards:
- Demand. A 1,000 sq ft vegetable garden needs roughly 600 gallons a week in a Midwest July.
- Dry spell. Pick the longest gap you want to cover — two weeks is usually sensible, three is comfortable.
- Storage needed. Two weeks at 600 gallons is 1,200 gallons, which is four and a half 275 gallon totes. Round up: five.
- Check the roof can fill it. 1,200 gallons needs about 1.8 inches of rain on a 1,200 sq ft roof. If your dry spell is followed by a half-inch shower, you will not refill in one event.
Yield table
| Roof area | Yield per inch of rain |
|---|---|
| 250 sq ft (shed) | ≈140 gal |
| 500 sq ft (garage) | ≈280 gal |
| 900 sq ft | ≈505 gal |
| 1,200 sq ft (house) | ≈673 gal |
| 2,000 sq ft | ≈1,121 gal |
| 5,000 sq ft (barn) | ≈2,804 gal |
| 10,000 sq ft (warehouse) | ≈5,607 gal |
At 0.623 gallons per sq ft per inch, times 0.9 collection efficiency. Roof plan area, not surface area — pitch does not change the catchment.
The six components that matter
- Leaf screen at the gutter. Cheap, and it prevents the single most common maintenance problem.
- First-flush diverter. Dumps the first 10–20 gallons, which carries most of the roof's accumulated contamination. $95 plumbed. Skip it only if the water is purely for ornamental use.
- Screened inlet. 1 mm mesh, sealed properly. Mosquitoes, not debris, are the reason.
- Overflow, screened and directed. A 2-inch standpipe near the top, piped away from foundations. An unscreened overflow is a mosquito farm.
- UV protection. A fitted sleeve at $38, or paint, or shade. HDPE chalks and embrittles in two Midwest summers, and sunlight also grows algae in the tank.
- Outlet at usable height. A tote on the ground gives you almost no head pressure. A 24-inch stand at $180 is the difference between a working drip system and a dribble.
Ganging multiple totes
Manifold them at the bottom on a common header with 2-inch bulkheads, not in series through the valves. A bottom manifold means all tanks share a level, fill together, draw together and let you isolate one for cleaning. Use unions so you can add a fourth tote later without cutting anything. We build these as a three-tote catchment bank for $1,180, or fabricate the manifold alone for $420.
Freeze protection
Water expands about 9% on freezing. A brim-full tote going into a Midwest winter will bulge against the cage and stay bulged. Either drain to 10% headspace, or drain completely and invert, or heat-trace and insulate if you need winter supply. The cheapest option is to drain in November and accept you are a three-season system.
Grade, clearly
Irrigation, livestock, washdown, fire reserve, dust control — technical grade, $95 to $145. Anything a person drinks or anything that touches an edible crop surface at harvest — food grade or rebottled, plus first-flush diversion, filtration and disinfection, plus whatever your jurisdiction requires. Do not economise on that second category.
A standard three-tote bank
- Storage
- 825 gallons
- Pad required
- ≈12 × 5 ft, level
- Totes, technical
- ≈$360
- Manifold, unionised
- $420
- First-flush diverter
- $95
- Overflow standpipe
- $78
- UV sleeves ×3
- $114
- Built and tested
- $1,180
Cost per gallon stored
- Technical IBC
- ≈$0.45
- 55 gal rain barrel
- ≈$0.65
- Purpose-built poly tank
- $2.10 – $3.40
- Buried cistern
- $4 – $9
Which is why most serious home systems end up being totes.
Harvesting questions
How much water does my roof actually produce?
Roof area in square feet × rainfall in inches × 0.623 × about 0.9 for collection efficiency. A 1,200 sq ft roof in a 1-inch storm yields roughly 673 gallons — which is two and a half 275 gallon totes from a single ordinary rain. People consistently underestimate this and then overflow their first tank in the first week.
Is harvesting rainwater legal?
In the great majority of US states, yes, and several actively encourage it with rebates. A few western states have historically restricted it under prior-appropriation water law, and Colorado in particular has specific limits on residential collection. Rules change; check your own state and municipality before you build, especially if you intend to plumb it into a building.
Can I drink harvested rainwater from a tote?
Not without treatment, and not from a technical-grade tote at all. Roof runoff carries bird droppings, dust, asphalt granules and whatever the roof is made of. For potable use you need a food-grade or rebottled tank, a first-flush diverter, filtration and disinfection — and in most jurisdictions a permit and a backflow preventer if it touches building plumbing.
What stops mosquitoes?
Physical exclusion, not chemicals. Fine mesh — 1 mm or finer — on every opening including the overflow and the vent, sealed properly rather than draped. A single unscreened 2-inch overflow will breed thousands of mosquitoes in a week, and it is the most common fault we see on home-built systems.
Give us your roof area
We will size the bank, name the grade and quote it built or as parts — whichever you prefer.