Install a rain sensor or turn the system off when it rains. Make sure that the spray patterns are adjusted and you are not watering the street. Again, early morning is the best time to water. Over watering can cause mold and mildew damaging your lawn and turning it brown. Don't over fertilize.
Fertilizer can burn the lawn requiring extra watering.
Consider xeriscaping your lawn. Choose the grass, shrubs, and trees that grow with the least amount of watering. The City of Helena is currently asking residents to voluntarily reduce their water usage. Conserving water helps the City Water Department and you. By conserving water and using it wisely you pay less.