The World Health Organization (WHO) issued a 2017 addendum to its fourth edition of the 2011 Guidelines for Drinking Water Quality (GDWQ), which includes new guidelines for perchlorate and barium and removes a 4-chloro-2-methylphenoxyacetic acid (MCPA) guideline for lack of significant risk from drinking water. Although trihalomethanes (THMs) were not updated in the 2017 GDWQ, they demonstrate some of the conceptual differences that occur between the GDWQ and USEPA MCLGs and MCLs. The new WHO guideline value for barium was increased to 1.3 mg/L from a level of 0.7 mg?L in the 2011 GDWQ. In the 2017 GDWQ, the new TDI for barium are currently 2mg/L. The 2017 GDWQ contains significant amounts of additional descriptive and background information on numerous topics, including chemical summaries, boil water notices, turbidity, water safety plans, management of cynobacteria, pharmaceuticals, and microbial risk assessment. The WHO guideline values for nitrate and nitrite are consistent with the USEPA MCLGs and MCLs, which are expressed as 10 mg/L nitrate and 1 mg/L nitrite to facilitate combining them at 10 mg/L as N. Methaemoglobinaemia is complicated by the presence of microbial contamination and subsequent gastrointestinal infection, which can increase the risk for bottle-fed infants significantly.
