Trade-Offs Between Continuous And Grab Samples For Water Quality In Distribution Systems

The design of sampling programs for water quality in distribution systems requires consideration of both temporal and spatial variability. Continuous water quality monitors represent a significant volume of sampling information in the temporal dimension at the expense of the spatial aspects of parameter variability. A simulated sampling methodology based on water quality modeling of real-world distribution systems was used to evaluate sampling designs incorporating different levels of grab and continuous samples. Systems with larger storage volumes exhibited greater temporal variation in chlorine concentration than systems with little storage. For systems with low temporal variability in water quality, continuous monitors did not improve the performance of the sampling program. A one-to-one exchange of continuous monitor samples for grab samples caused a significant decrease in the performance of the sampling program. For systems with higher temporal variability, the use of continuous monitors improved the efficiency of the sampling program only when located at areas of high temporal variability. The findings illustrate the need for system-specific knowledge and careful evaluation of sampling design before the implementation of continuous monitoring systems.