Water can become corrosive at lower pH values. In addition, the corrosion treatment chemical added to the water, orthophosphate, works best at a pH range of 7.0 to 8.0. The Washington Aqueduct is required to maintain a pH between 7.4 and 8.0 for water leaving the treatment plant. DC Water monitors the pH in the distribution system daily to ensure these levels stay within the optimum range for orthophosphate. DC Water has set a target range of 1.0 to 4.5 mg/L orthophosphate to target in the distribution system.

The graphs below shows the maximum, average, and minimum results for pH on a monthly basis and orthophosphate on a quarterly basis. The top and bottom of the lines represents the maximum and minimum values. The black dash in the middle of the line represents the average value.