18. The person in charge of a distribution system that supplies chlorinated water must, for the purpose of testing for the trihalomethanes referred to in Schedule 1, collect or have at least 1 sample of the water supplied collected during each of the quarters beginning respectively on 1 January, 1 April, 1 July and 1 October, with a minimum interval of 2 months between samplings.
Notwithstanding the preceding paragraph, if the aforementioned system supplies only a tourist establishment, a health and social services institution, an educational institution, a correctional facility or several such establishments, institutions or facilities, the person in charge of the system is required to collect only one sample of the water supplied per year for the purpose of testing for trihalomethanes, between 1 July and 1 October or, if the establishment, institution or facility is not in service between 1 July and 1 October, at any other period when it is in service.
For the purposes of the calculations of the standards of quality set out in Schedule 1 as regards total trihalomethanes, the person in charge must take the average of the values obtained in the preceding 4 quarters. If in any one quarter more than 1 value is obtained, the person in charge must average the values and use the result obtained as the value for that quarter.
O.C. 647-2001, s. 18; O.C. 467-2005, s. 18.