Harvesting the rain can save on your water bills and provide natures own untreated city water to plants. It’s can also be a lot of fun!
There are many ways to accomplish this, the most common perhaps is by using rain barrels or a cistern, but there are others. For example, reducing paved or impermeable surfaces on your property is one way, or capturing the rain via catch basins that runoff from them. Mulch basins, having trenches, built-up soil or terracing can direct also water to needed plant materials & trees rather than going down a storm drain. Be mindful however to keep all water away from your foundation.
Check out this publication from Canada Mortgage & Housing (CMHC) on Collecting & Using Rainwater at Home.