Chemical cleaning of water systems can be divided into two classifications: pre-operational and remedial. Pre-operational cleaning is performed to prepare the water-contacted metal surfaces to receive chemical treatment, which provides protection from scale, corrosion, and microbiological growth. Remedial cleaning is performed to restore water systems that have been fouled with scale, corrosion products, and microbiological growth due to inadequate or ineffective water treatment. Cleaning, particularly remedial-type cleaning, is often performed by outside contractors familiar with cleaning procedures, techniques, and safety. It should be noted that if the water system is significantly scaled, the chemical treatment program was obviously inadequate and was not properly designed, set-up, controlled, or applied.
After cleaning has been completed, the chemical treatment program and quality control (QC) program must be improved so the same problem does not recur. Use of a well-designed quality assurance (QA) program would have produced identification and notification of potential and developing problems before they became serious. Preoperational cleaning is often performed by contractors responsible for the fabrication of the water system before turning it over to the owner. Water system operations personnel must assess the effectiveness of any cleaning process that has been performed.