Determine your needs: By understanding what you’re planning on using your rainwater for, you can determine how much you need to store and collect. Common uses are gardening, showering, sinks, and toilets. 
Calculate rainfall: There are plenty of online resources that can tell you what the average annual precipitation is in your location. An approximate average throughout Ontario is 35 inches of rain. You can then calculate the square footage of your collection area and your rainfall to get an approximate quantity of available water. An average house in Ontario can collect up to 40,000 USG annually.
Size your cistern: Based on your needs and rainfall, choose an appropriate size. The size of your cistern will depend on the amount of rainfall you receive, the size of your roof, and your water usage. A general rule of thumb is to have enough storage to last you through the dry months. Poly cisterns are available up to 1700 USG, and Concrete cisterns up to 6,000 Gallons. You can learn more about water consumption levels on our Cistern overview article here.
Placement: Cisterns can be placed above or below ground. Above-ground cisterns are easier to install and maintain. They are most frequently used for gardening, and are typically gravity-fed without the use of a pump. You can choose from a variety of liquid storage tanks for this purpose, as they don’t need to handle the weight of being buried. Below-ground cisterns are more aesthetically pleasing, but they require more excavation and planning.
Filtration: Plan for a system to remove debris and contaminants. We recommend your primary filter options be installed on the gutters.