The ads promised a shower that feels like a tropical waterfall, and they showerheads delivered on the promise. That's why the city of Seattle is seeking federal sanctions against the manufacturer. Federal law requires that shower heads not exceed flow rates of 2.5 gallons of water a minute. But the five models tested by Seattle Public Utilities had flow rates of 7.62 to 13 gallons per minute. "This has the potential to significantly undermine all our efforts to encourage and achieve water conservation," said Al Dietermann, a conservation official with the utility.