If you're buying a property that contains rental units, consider obtaining a letter from a real estate broker or some other documentation verifying that the rents you plan to charge would be realistic. A lender who is qualifying you for a mortgage probably will not take your word for that.
When water flows backward through the water supply system, it is called backsiphonage or backflow. When that water is accidentally mixed with hazardous chemicals or bacteria, it is called dangerous! For this reason, never use spray attachments without a backflow prevention device. The chemicals used on your lawn are toxic and can be fatal if ingested.