Until 1970s most people obtained and consumed water from the hand dug wells, ponds, rivers or canals. These water were usually consumed without any treatment. Therefore, epidemics of diarrhoea and other water-borne diseases were very common. Hundreds of people particularly the infants died only because of drinking these unsafe water. To assure the safety of drinking water, different countries of the world set drinking water standards but great miseries arises in non-developed and developing countries due to lack of their knowledge about safe drinking water and also for their economic and overall conditions. Это и многое другое вы найдете в книге Drinking Water Quality and Standard (Md. Haque)