Monitoring for Cryptosporidium before implementation of the United States Environmental Protection Agency's Long Term 2 Enhanced Surface Water Treatment Rule (LT2) provides several benefits that will not be available after formal monitoring begins. The main advantage for public water systems to "grandfather data" is to gain additional time for planning and implementation of treatment changes, should Cryptosporidium concentrations warrant treatment modifications in accordance with the LT2. Because Cryptosporidium concentrations may fluctuate across years, additional data collected during the period leading up to rule implementation may provide a more representative indication of the Cryptosporidium concentrations than the minimum 2 years of monitoring. Monitoring before rule implementation provides an opportunity for utility staff to first conduct practice sampling to familiarize themselves with monitoring activities without the risk of a monitoring or reporting violation. In addition, laboratories are likely to be more available before the rule to accommodate utility preferences for sampling dates than during the rule. Includes 2 references.