The Region of Waterloo relies on a network of over 100 supply wells for the bulk of the Region’s municipal water supply. The Region has long conducted monitoring of supply wells and monitoring wells to support sustainable water taking from a variety of local aquifers. Recently, the considerable monitoring data collected by the Region was a key resource in completing early requirements of the new Ontario Clean Water Act. Tammy will highlight how the Region’s chemical and water level groundwater monitoring programs have changed, and continue to change, in response to contamination events, legislation, technology, and the anticipated Source Protection Plans under the Clean Water Act. The evolving groundwater monitoring programs at the Region can provide examples of best management practices, and “lessons learned”, for other municipal or large groundwater monitoring programs.