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The World Health Organisation (WHO) has issued new safety guidelines for drinking water that put the emphasis on prevention of waterborne disease rather than responses to outbreaks.

Currently, water sanitation relies largely on testing water samples for chemical and biological contaminants, but this often means that pollutants are identified long after the water has been consumed.

Instead, says the WHO, regulators should ensure water quality by protecting water sources and controlling treatment processes 'from source to tap'. This approach can be applied to any setting, whether isolated rural situations such as settlement camps or urban centres with running water.

The WHO guidelines will help reinforce one of the UN Millennium Development Goals, which is to halve the number of people — currently 2.6 billion, mostly in developing countries — without access to safe water and basic sanitation by 2015.

Earlier this year, more than 4,000 people suffered from acute diarrhoea and 34 died in Hyderabad, Pakistan, when highly polluted water from a lake contaminated an adjacent water supply.

In Bangladesh, ground water containing high concentrations of arsenic puts millions at risk of severe health problems such as skin lesions and cancers of the skin, bladder and lung. In response to threat such as this, the updated guidelines also include recommended safe values for 100 chemicals based on a review of fresh scientific evidence.

Safety of drinking water can also be highly compromised in emergencies, because of inadequate sanitation and hygiene, says the WHO. Floods, for example, can contaminate wells with sewage, and drought can force people to use unsafe water when their usual sources dry up.

The WHO's advice includes several low-tech preventive measures that people can use in their own homes — such as covering stored water to prevent its contamination by human and animal waste, and boiling water before drinking it. But according to John Fawell, a UK consultant on drinking water and environment, larger scale water supplies will need a more technological approach.

"Both filtration and chlorination are important for ensuring the removal or inactivation of bacteria and viruses, and filtration is the key against parasites such as cryptosporidium," Fawell told SciDev.Net. "Here, the use of portable kits to take measurements frequently — hourly rather than daily — can be a powerful tool."

During this year's Hyderabad crisis, health problems were compounded by the fact that sanitation officials had been over-chlorinating the water in an attempt to deal with the contamination. The WHO emphasises that educating local individuals responsible for sanitation is crucial.

Reinforcing the need for local training Fawell says: "the composition of raw water can change, for example after rainfall, and understanding the science of how a particular treatment works is key to adapting it to different conditions".

Link to the full WHO guidelines

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