A system automatically maintains at least one of a pH level and a sanitizing agent level of water in a water feature. The system includes a sensor assembly responsive to at least one of a pH level of the water and a sanitizing agent level of the water. The system further includes a controller which generates control signals in response to signals from the sensor assembly. The system further includes at least one of a first source containing an sanitizing agent material and a second source containing a pH-modifying material. The system further includes a third source comprising a valve assembly and a third container containing a liquid calibrant material. The valve assembly is responsive to at least a portion of the control signals from the controller by selectively allowing the calibrant material to flow from the third container through the sensor assembly to the water feature.