Nev. Admin. Code § 445A.529
A supplier of water that has installed a system for treatment before November 29, 1990, which does not consist of technologies pursuant to which the supplier of water shall treat water in compliance with NAC 445A.521 or which was not designed to comply with the operating criteria in NAC 445A.531 and 445A.533, shall submit to the Division or the appropriate district board of health an engineering report which demonstrates that the plant can be operated to supply water meeting the requirements for performance contained in NAC 445A.521 and 445A.526. This report must include an analysis of the previous 12 months of operating data and any special studies conducted to test the performance of the plant under conditions of adverse water quality.
Nev. Admin. Code § 445A.529
NRS 445A.860