What your average water bill? If I leave my sprinkler system to water everyday 5 days a week (M-F), my bill is usually around $190 - $200. I have sandy soil, so watering 2 days a week like most of you do, doesn't cut it for my lawn. I haven't had it on for the last 10 days (rained 8 of the last 10 days) but I am trying to go M-W-F after all of this rain and see how it affects my lawn and bill. I roughly figured that watering 5 days a week for 4 weeks (20 days) costs me about $7.50 a day.