The best place to install your rain barrel is near where you need to use the water. Since rain barrels supply low-pressure water, keep in mind that flow rate decreases as it empties and it is necessary to elevate the barrel to improve flow rate. If your water use requires more water pressure, you could always invest in a pump, but this is not necessary for such uses as drip irrigation. The low pressure is not suited for hose-end sprayers and sprinklers and you should, therefore, consider such options as garden hoses, water cans, and soaker hoses.
To estimate how much rain water you will capture, the rule of thumb is that you get half a gallon per square foot for 1 inch of rainfall. However, factors like the slope of the roof and the placement of the downspout also affect the amount of water captured.
You should make plans for overflow given Ontario’s high rainfall levels. Direct the overflow away from your home’s foundation. This could be through an overflow outlet or through a hose to drain the overflow. If you have the space, you could link barrels to collect even more water.
Zinc and other chemicals are often applied on roofs to fight algae and moss. If this is the case for your roof, or if your roof/gutters are made of copper, do not use the runoff on edible plants