4.3.1. Water Treatment Technology and Regulations

While drinking water regulations have continued to evolve since 2006, they have had varied influence on the treatment of Delta source waters. The shift from chlorination as a primary disinfectant toward ozonation has continued since 2005. By 2020, about 85 percent of the combined treatment capacity of the participating agencies employed ozonation (Figure 2). In the current era, drinking water regulations have played a reduced role in driving MWQI program activities. However, that trend would likely reverse if new regulations were implemented. Examples of new DBPs being considered for regulation include four additional brominated HAAs and nitrosamines (such as N-nitrosodimethylamine or NDMA) [113]. In waters high in bromide, such as Delta waters, the five currently regulated HAAs may only represent around half of the concentration of the nine HAAs [114]. Certain pharmaceuticals discharged from wastewater treatment plants react with chloramines to form NDMA in drinking water [115]. The participating MWQI agencies that use ozone as the primary disinfectant use chloramines as the secondary disinfectant; thus, NDMA is produced at many of their water treatment plants.
