In April of 2022 we installed three used 275-gallon totes behind the office shed and plumbed them off the north gutter of our main shop roof. Eight hundred and thirteen square feet of corrugated steel, sloped about seven degrees, drains into one 4-inch downspout. We metered the inlet and the outlet. Here is what twelve full months of data said.
The setup, in plain terms
- Three used 275-gallon totes plumbed in parallel with a common overflow.
- First-flush diverter at the top of the downspout — about 2 gallons of flush per storm.
- 60-mesh screen at the inlet, rebuilt every eight weeks.
- Inline ball valve, then a short run to a battery-powered demand pump used for cage wash-down water.
What the roof produced
Pittsburgh averages 38.2 inches of rainfall annually. At 0.623 gallons per square foot per inch of rain, a theoretical maximum for an 813-square-foot roof is about 19,300 gallons a year. The brochures would stop there. The meter did not.
Actual captured volume for the 12 months ending March 2023: 14,840 gallons. The gap — about 4,400 gallons — is the combined loss from the first-flush diverter (roughly 180 gallons), evaporation and screen cleaning loss (about 220), and overflow from storms that arrived faster than we could pump the tanks down (about 4,000). The last item was the biggest surprise. We don't need more roof. We need more storage.
What we used the water for
In a wash yard the demand curve is steady and not picky about potability. The rainwater went to:
- Cage pre-rinse before the hot caustic stage — about 8,200 gallons over the year.
- Truck tire wash-down at the gate — about 2,400 gallons.
- Garden irrigation on the back plot — about 1,100 gallons.
- Spills and incidental cleanup — the rest.
Was it worth it?
Here is the honest accounting. The three totes were inventory we weren't going to sell — Grade C with cage rash. Wholesale value was negligible for all three. Plumbing, screen, pump, and first-flush hardware cost a couple hundred out of pocket. Labor was one Saturday plus another weekday afternoon for fixes.
The system saved us 14,840 gallons of metered city water over the year — a modest but real offset at our commercial rate. Payback is four and a half years. On totes we otherwise would have stored or shredded.
For a homeowner paying residential water rates, the payback is longer, but the side benefits (soil health, emergency storage, hose-bib independence) outlast the math. We now run six tanks behind the shed. We have not paid a water bill for cage pre-rinse since June 2022.