United Utilities Group PLC (LSE:UU.) is at the heart of a legal challenge against Ofwat, with environmental group River Action accusing the regulator of unlawfully passing the cost of long-term industry failings onto customers. The group plans to file a legal claim against the regulator this month, it said in a statement, arguing that average 36% bill increases approved by Ofwat in recent months could be used to rectify infrastructure issues that should have been addressed years ago. River Action contends that this approach could result in customers effectively paying twice, as regulations state that the public should not bear the cost of bringing water companies into compliance with their existing permits. These rules include limits on raw sewage discharges and requirements for properly functioning treatment works. The legal challenge specifically targets funding allocated to United Utilities for wastewater treatment works and pumping stations in the Lake Windermere area.