Precautionary Localized Boil Orders are issued to water customers when pressure in the distribution system drops below 20 pounds per square inch (PSI). Precautionary Localized Boil Orders are issued because it is possible, but unlikely, that bacteria can enter the water system when pressure in the line drops below 20 PSI. The boil order is “precautionary” because there is no evidence of contamination. The boil order is “localized” because only a relatively small portion of the system has experienced a pressure drop below 20 PSI. 35 Illinois Administrative Code Subtitle F Section 607.103 requires the issuance of Precautionary Localized Boil Orders when pressure in the system is reduced to below 20 PSI.