Two fed from the front gutters. The slight difference in elevation allows the overflow from the one to fill the other.
The plan is to buy a large (250 gallon) water tank with a more horizontal profile (for safety) and place it below the other two with a similar overflow system. On one rainy weekend we could pretty much be set for a month without rain.
We use the barrel connected to the gutters in the back to direct water or to fill a watering can. The on/off switch is just hanging the end of the hose above the level of the water in the barrel.
Last year we only watered from our city water supply once. This May was very dry and so we ended up using our tap water three times. (Thus the desire to buy a larger tank) Our water department not only encourages the use of rain barrels, they sell them at a discount.
It works pretty well. We have 6 fruit trees, 8 raised beds, various potatoes and tomatoes in pots, 3 grape varieties, hazelnuts, blueberries, strawberries, and some herbs scattered in a 35′ x 45′ backyard in the middle of the city. (Our neighbor, the lawyer, keeps saying he’s going to do something with his area for his employees. So far…)
After the light, ours is the third townhouse on the left. Who would think that such an oasis exists in behind the street wall?