A running toilet is one of the most quietly costly problems in an Arizona home. Depending on severity, it can waste between 6,000 and 120,000 gallons of water per month – adding anywhere from $27 to over $500 to your bill without a single extra flush. In Tempe and Mesa, hard water from Maricopa County’s supply accelerates flapper wear, making this more common than homeowners expect. The fix is often simple and cheap if caught early: a $10 flapper replacement and a quick adjustment. But if the flush valve seat is corroded or the fill valve has failed, professional repair is the smarter move before months of waste stack up. Understanding what’s actually happening inside the tank – and knowing when to stop guessing – saves real money in 2025.