LT1ESWTR was the first small system regulation that provides protection against the disease-causing organism Cryptosporidium. In Pennsylvania, the LT1ESWTR is expected to provide additional protection to over 600,000 customers. This rule will applies to about 265 public water systems using surface water or ground water under the direct influence of surface water that each serve less than 10,000 people. Early provisions of this rule took affect in the summer of 2002, but the main provisions becameeffective in 2005.