This is the 1000 gallon tank we installed this year, hooked up directly to the gutter. We missed the heaviest of last weekend’s rain, but there was still plenty over the following 24 hours from when we got it hooked up. We quickly learned that there is much more into figuring out how much you can capture off your roof than knowing how many square feet are emptying into the tank.
First off, you see how short the pipe is? but it is steep, and it is also only 3”. A steep pipe will let water flow quicker than a shallow pipe, so water won’t back up and flow over rather than down – but a 3” pipe won’t let as much water pass as a 4” would! So during a heavy rain, the drain pipe might not handle the water quick enough and a lot will be lost over flowing the gutters. During a real gully washer, and we had that just before we hooked up the tank, the gutters couldn’t handle the volume of rain at all and it overflowed the gutters everywhere!
That means a 1” rain, falling in 20 minutes, won’t even begin to put water in the tank with normal gutters and collection system.
The bottom line is, off about 400 square feet of roof, over 24 hours, we collected about 50 gallons of rain. That just about makes it up to the bottom bib! If we’re lucky, we’ll get more rain before the summer monsoons, but will not hold my breath! We were lucky to get the rain last weekend.
but winter rains were enough to fill our 350 gallon tank, and the rain last week topped it off from where I’d taken some for watering the garden.
Now we are collecting rain water, I’m using my dechlorinating system, via the hose, for one good watering a week or so (as needed) and then shallower watering from the rain barrels. With lots of seedlings, still having shallow roots, I’m keeping the surface moist.