Id say because its not potable, it most likely has no chlorine in it which is used to kill bacteria and harmful minerals. It doesn't mean it isn't good for your plants. I bet its probably better for em. Huge stadiums and Golf Courses use non-potable water to water their huge playing fields, and they have some of the greenest grass I have ever seen. If using non potable water, Id HIGHLY suggest purchasing a good TDS/ECM meter. This will tell you how many Total Dissolved Solids and the Electrical Current of your water. Something beneficial for you, your animals, and your plants.

If not purchasing the Meter, leave it unboiled and use it like normal.