The measurement and control of pH is critical to the safety and comfort of the occupants. For example, if the pH is too low, pool and spa occupants may experience skin and eye irritation or even respiratory issues. If the pH is too high, chlorination (disinfection) may be less effective, and the water may be more prone to cloudiness, odor, and scale formation. Pool and spa environments typically measure pH continuously in larger commercial control systems but may also be measured by a service provider with grab-sample methods. Common performance challenges can be mitigated with the optimal sensor design, in particular the reference junction design, housing material, and sensing chemistry.