Drinking water is defined as water intended for human consumption for drinking and cooking purposes from any source. It includes water (treated or untreated) supplied by any means for human consumption.Safe drinking water is a basic amenity but while cities could have access to safe and hygienic water, several Indian households, especially in semi-urban and rural areas are not so fortunate.
There are several reports which state that waste water from industries and other effluents and sewage are constantly dumped into rivers making the waters of these rivers dangerous for drinking. Similarly, groundwater sources in some belts of India have contaminants like arsenic above the required parameters, which makes it unsafe to drink.In India water is affected not only by contaminants but also with excess iron fluoride, salinity and nitrate besides arsenic. Further, every year lakhs of cases diarrhoea, typhoid cases and viral hepatitis are reported which result in most cases from unclean and unhygienic water supply and poor sanitation.
The quality standards for drinking water in India is prescribed by Bureau of Indian Standards (BIS) laid down IS 10500: 2012.The Bureau of Indian Standards originally published the Indian standard for drinking water IS 10500 (Drinking Water-Specification) in the year 1983. Since then the standard has undergone few revisions with the last one being carried out in the year 2012. The 2012 revision was undertaken to upgrade the requirements of the standard so as to align them with the internationally available specifications on drinking water. The revisions have also taken into account the updated information available about the nature of the contaminants as well as the latest methods for identifying and determining their concentration.
Proper control measures and routine testing and analysis of drinking water supplied by Jal Boards and other agencies supplying drinking water,is carried out to ensure water quality and prevent risk from certain pathogens. The frequency of testing drinking water is laid down and it also depends on the raw water quality. Water is also tested when there are noticeable impurities or there are changes in colour or taste of the water.While it is necessary to take precautions to prevent contamination of drinking water, but testing must also be undertaken for chlorine resistant parasites that can get into water like cryptosporidium species and giardia.
In an ideal situation all samples of water taken from the water distribution system which includes consumers’ premises, should be free fromcoliform and other biological organisms and bacteriologicalquality must be as per BIS standards. Bacteriological quality of drinking water includes absence of e.coli in 100 ml sample. Biological examination is also valuable when determining thecauses of objectionable tastes and odours in water. Without doubt drinking water must be free from microscopic organisms such as algae, zooplanktons, flagellates, parasites and toxin producing organisms in order to be safe for drinking, cooking and processing of foods.
The 2012 revision in BIS standards has laid down the specifications for virological requirements also. Addition of virological requirements in the 2012 revised standards is one of the most significant changes made by BIS. MS2 phage are indicators of viral contamination in drinking water and for water to be safe for drinking MS2 phage shall be absent in 1 litre of water. The standard now clearly states that all samples taken from the distribution system including consumer premises should be free from viruses.
According to Central Ground Water Board, BIS IS 10500:2012 the quality of water has standards with two limits “acceptable limits” and “permissible” limits which is applied in the absence of an alternate source of water. If any parameter exceeds the limits set by BIS then the water is considered unfit for human consumption. In broad terms, if the water is bacteriology contaminated by E-coli or virusesor if chemical contamination exceeds maximum permissible limits as prescribed in the standards for water then BIS considers that water to be unfit for drinking and unsafe.
Maintaining the quality of water is a major challenge but regular water testing and analysis, surveillance and monitoring by recognised water quality testing laboratories with qualified manpower and latest testing equipment can help to overcome the challenge.According to BIS 10500: 2012 the acceptable limit of bacteria and other major contamination are outlined below in brief.
Organoleptic and Physical Parameters
Colour Hazen units max
Extended to 15 only, iftoxic substances are notsuspected in absence ofalternate sources
a) Test cold and whenheated
b) Test at several dilutions
Test to beconducted onlyafter safety has beenestablished
Turbidity NTU Max
Total dissolved solids mg/l Max
NOTE — It is recommended that the acceptable limit is to be implemented. Values in excess of those mentioned under ‘acceptable’ render the water not suitable, but still may be tolerated in the absence of an alternative source but up to the limits indicated under ‘permissible limit in the absence of alternate source’ in col 4, above which the sources will have to be rejected.
Safe drinking water must fulfill the standards under general parameters concerning substances undesirable in excessive amounts like aluminium, ammonia, barium, boron, calcium chloride, copper, fluoride, iron, magnesium, nitrate, silver, sulphate, zinc, etc.
Water is safe to drink if parameters concerning toxic substances like cyanide, lead, mercury, nickel, pesticides, total arsenic, etc. are within the prescribed limits.
Safe drinking water must also be within limits for the following parameters
- Radioactive substances like Alpha and Beta emitters,
- Pesticide residue limits
http://cgwb.gov.in/Documents/WQ-standards.pdf BIS standards