Cold water or iced juices appear tempting in the sweltering heat but it often comes contaminated with bacteria, viruses, minerals and heavy metals, which not only cause gastro-intestinal trouble but also skin and eye disorders.
Gunjan Sharma, 22, a PR professional learnt her lesson the hard way, and now she is so conscious about the quality of water she consumes that even her gol-gappas are filled with mineral water.
"I had once consumed regular water from outside and suffered for a week with gastroenteritis. To this day, I only drink mineral water when I'm out," she said.
Waterborne diseases are infectious diseases that spread primarily through contamination in water. They spread either directly from drinking unclean water or coming into contact with such water and through flies or filth.
"Most intestinal (enteric) diseases are infectious and are transmitted through faecal waste that contains pathogens - which include viruses, bacteria, protozoa, and parasitic worms," said Dr Umesh Kapil, professor, Gastroenterology, All India Institute of Medical Sciences.
These disease-causing germs travel through water sources and interfuse directly through people handling food and water.
"Since these diseases are highly infectious, extreme care and hygiene should be maintained by people looking after an infected patient. Hepatitis, cholera, dysentery, and typhoid are the most common waterborne diseases," Dr Kapil said.
Maulana Azad Medical College conducted a city-wide study aimed at assessing water and hygiene-related attitudes and practices, and quality of water in urban slums of south Delhi in July 2013.
Around 83% participants perceived gastro-intestinal tract infection as the most important health problem. Around 75% participants did not use treated water before drinking it while 45% participants consumed water from privately-owned tube well/ borewells.
According to the study, water shortage usually lasted two days or more at a stretch with severe scarcity occurring twice a year. About 45% participants had toilets within their households and around 53% of the drinking water samples collected from storage containers showed positive bacteriological contamination. Women aged 15 years and above were largely responsible (93%) for fetching water, found the study done across four urban slums of south Delhi.
Industrial and biological pollution are the main reasons for water contamination in India, say experts.
"Rivers and water bodies are contaminated with toxic chemicals such as cadmium, arsenic and lead in industry effluents that poison our lungs and brain. The government does not factor in public health while drafting policies for environmental pollution. Public health cannot work in isolation. It should also be linked with water contamination and air pollution and people must be trained and educated about it," said professor TK Joshi, director, Centre for Occupational and Environmental Health at Maulana Azad Medical College.
"The UK has adopted four simple measures to keep environmental pollution under control and this policy has been rated as one of the best methods to keep the environment clean. The four measures include adequate amount of clean drinking water for every citizens, safe disposal of waste, proper nutrition for the citizens and planned and proper housing for all its citizens," said Dr Joshi.
Contamination of drinking water supplies can occur at the source as well as through the distribution system.
"Water contamination also leads to fungal infection of the feet and toes, bacterial infection leading to boils all over the skin and the commonest thing among children is viral warts," says Dr RK Joshi, skin specialist at Indraprastha Apollo hospital.
"Protozoan infection or acanthomoeba infection in the eye could be caused due to contamination of water. It can develop in people who usually wear contact lenses. Apart from this fungal and bacterial infections in the eye due to water are common," said Dr JS Titiyal, professor, RP Centre of Ophthalmology, AIIMS.
The reverse osmosis (RO) system is the best method to treat water and keep it safe.