Household Water Treatment and Safe Storage (HWTS)

Over one billion people still lack access to safe drinking water today. Waterborne diseases caused by consumption of unsafe drinking water are a major health burden in most of the developing countries in the world. Lack of safe water perpetuates poverty. Safe drinking water and sanitation are the condition for physical health and intellectual, social and economical activity and development.

The quality of drinking water being supplied is often neglected even if the access to water supply has been increased substantially. However, drinking water supplied by centralised treatment systems is likely to get contaminated due to poor distribution networks, management and unhygienic handling prior to consumption.

To treat the water at household level in order to assure the microbial (and chemical) quality together with safe water storage and proper hygiene practices could considerably contribute to reach the millennium development goals. Household-level Water Treatment and Safe Storage (HWTS) can reduce episodes of diarrhoeal diseases by 39% (WHO 2007a). According to the WHO (WHO 2007b) HWTS dramatically improves microbial water quality; significantly reduces diarrhoea; is among the most effective of water, sanitation and health interventions; is highly cost-effective; and can be rapidly deployed and taken up by vulnerable populations.

HWTS is a multi-barrier approach and there are several steps in HWTS which all contribute (adapted from CAWST 2009):

Using the multi-barrier approach is the best way to reduce the risk of drinking unsafe water. We need to follow a process and not just rely on a single technology to improve water quality. Both community and household water treatment systems follow the same water treatment process. The only difference is the scale of the systems that are used by communities and households.

Source protection

Risks, which may threaten drinking water quality at the source or point of collection include: poor site selection or protection; poor construction and deterioration or damage to structures; and lack of hygiene and sanitation knowledge in the community. Actions that can be taken at the community level to eliminate these risks can include: regularly cleaning the area around the water source; moving latrines away from and downstream of water sources; building fences to prevent animals from getting into open water sources; lining wells to prevent surface water from contaminating the ground water; building proper drainage for wastewater around taps and wells.

Sedimentation

Sedimentation is a physical treatment process used to reduce the turbidity of the water (see also sedimentation). Suspended materials in water, such as particles of sand, clay, and other materials can be substantially removed simply by settling the water. This can be done by using a natural reservoir, a settling pond, or a large tank. The sedimentation process can be accelerated through the use of coagulants and flocculants. These are natural (e.g. Moringa) and synthetic (e.g. purifier of water, PUR) chemicals that change the electrical charges of the suspended materials. This allows the particles to join together, thereby increasing their mass so that they settle to the bottom of the container. Since bacteria and viruses are often attached to particle surfaces, the removal of particles through sedimentation will produce a marked reduction in bacterial concentrations.

Filtration

Filtration is commonly used after sedimentation to further reduce turbidity and remove pathogens. Filtration is a physical process which involves passing water through filter media. Filters remove pathogens in several ways. These include straining, where the particles or larger pathogens such as worms become trapped in the small spaces between the grains of filter media; adsorption, where pathogens become attached to the filter media; or biological processes, where pathogens die naturally or the microorganisms living in the filter consume the pathogens.

There are various types of filters that are used by households around the world including ceramic candle filters,  colloidal silver filters, biosand filters, cloth straining, biosand filters adapted for arsenic removal, membrane filters (e.g. lifestraw), etc.. Sand and ceramic are the most common filter media, although cloth filters are also often used. 

Disinfection and pasteurisation

The destruction of the organisms’ cell walls by oxidation is known as disinfection. Typically, disinfection involves the addition of chemicals such as chlorine. It can also be induced by ultraviolet radiation, such as natural sunlight or artificial UV rays. The most common methods used by households around the world to disinfect their drinking water is chlorination.

Heat can also kill microorganisms and this process is called pasteurisation. Pasteurisation has almost the same effect as disinfection. The most common methods to pasteurise water are boiling, solar disinfection or solar pasteurisation.

If water contains high amounts of organic matter (for instance surface water from tropical regions), there is a risk of the formation of toxic disinfection products when chlorine reacts with these organics. Turbid water helps pathogens to “hide” from chemicals and natural or artificial UV radiation. Reducing turbidity and organic matter by sedimentation and filtration before the treatment  is therefore necessary to improve the effectiveness of these disinfection methods.

Safe storage

Households do a lot of work to collect, transport and treat their drinking water. Now that the water is safe to drink, it should be handled and stored properly to keep it safe. If it is not stored safely, the treated water quality could become worse than the source water and may cause people to get sick. Safe storage means keeping treated water away from sources of contamination, and using a clean and covered container. It also means drinking water from the container in a way so that people do not make each other sick. The container should prevent hands, cups and dippers from touching the water, so that the water does not get re-contaminated.

There are many designs for water containers around the world. A safe water storage container should have the following qualities:

• Strong and tightly fitting lid or cover
• Tap or narrow opening
• Stable base so it does not tip over
• Durable and strong
• Should not be transparent (see-through)
• Easy to clean

Regarding the safe storage of water, disinfection with chlorine has a advantage over the other methods, as chlorine has a residual effect.