It means the drinking water system either lost pressure or the pressure dropped below 20 psi. Illinois EPA mandates water used for consumption (e.g., drinking, cooking/preparing food, etc.) should be boiled before use for a minimum of 24 hours after the water has been restored. Testing is needed to verify the drinking water system has not been compromised during the drop in pressure. Illinois EPA mandates boil orders be imposed for a minimum of 24 hours starting when repairs are completed.