I put four 80-gal. black plastic tanks on the southfacing wall of my greenhouse, as a passive heatsink and also a source of water for the plants.
The original plan was to funnel rainwater collected from the roof gutters to the tanks, but I noticed that magpies were carrying dog poop up on the garage roof to pick it apart. Didn't really want all that dog poop draining to the tanks, where the bacteria would bloom in the warm (65-70°F) water: dog poop soup.
So I fill the heatsink/watering tanks with the garden hose.
