The Idyllwild Water District and Pine Cove Water District are small groundwater systems with multiple wells. Both systems have soft, mildly acidic waters with high carbon dioxide content and dissolved inorganic carbon concentrations of approximately 18 mg/L C, and both systems exceeded one or both of the lead and copper action levels in 1993 and 1994. In 1997, aeration was investigated to increase pH and replace inhibitor or other chemical additions. Four designs were evaluated, and a deep bubble aeration system was pilot‐tested. Full‐scale systems were designed and built and became operational in October 1998. Aeration raised the pH from 6.1–6.3 to 7.1–7.6, and by January 1999, both systems easily met both the lead and copper action levels. Radon (Rn) samples taken at Pine Cove showed a 99% reduction to 33 ± 8 pCi/L, assuring compliance with the proposed Rn regulation. Using aeration for corrosion control has considerably simplified treatment and improved water quality in most respects. Treatment was integrated with system designs, enabling the use of one treatment plant for the multiple wells at each system, locating the treatment plants above storage to eliminate repumping, and maximizing electricity savings by increasing operation at off‐peak times.