The best ways to clean water are found in a multi-barrier approach that protects water quality from source to consumption.
Note: The content on this page has been adapted from publications of World Health Organization (WHO) and Centre for Affordable Water and Sanitation Technology (CAWST).
The Multi-Barrier Approach for HWTS
The World Health Organization has determined that a multi-barrier approach to household water treatment and safe storage (HWTS) is the best way to reduce the risk of drinking unsafe water.
A multi-barrier approach means ensuring that water is protected and purified every step of the way from the water source to household storage and consumption. Water quality will only be as good as the weakest link in the chain of water handling.
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.
Introduction to HWTS
Step 1 - Water source protection
Step 2 - Sedimentation
Step 3 - Filtration
Step 4 - Disinfection
Step 5 - Safe water storage
Step 1 - Water Source Protection
There are many pollution problems which may threaten drinking water quality at the source, or point of collection. These risks include the following:
* poor site selection
* poor protection of the water supply against pollution
* poor construction
* deterioration or damage to structures
* lack of hygiene and sanitation knowledge in the community
Protecting the water source reduces or eliminates these risks and can lead to improved water quality and health. Actions that are good ways to clean water and that can be taken at the community level can include some of the following:
* 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 welts
Click here to read more about water source protection.
Step 2 – Sedimentation
Sedimentation is a physical treatment process used to reduce the turbidity of the water. Remember that turbid water looks cloudy, dirty, or muddy and is caused by sand, silt, and clay that are floating in the water.
Turbid water usually has more pathogens so drinking it increases your chances of becoming sick.
There are ways to clean water and reduce turbidity by simply letting the water settle for some time.
This can be done in a small container such as a bucket or pail.
The sedimentation process can be quickened by adding special chemicals or native plants, also known as coagulants, to the water.
Coagulants help the sand, silt and clay join together and form larger clumps, making it easier for them to settle to the bottom of the container.
Three common chemicals used as ways to clean water and aid in sedimentation are aluminum sulphate, polyaluminum chloride (also known as or liquid alum) and ferric sulphate.
Native plants are traditionally used in some countries in Africa and Latin America to help with sedimentation. For example, prickly pear cactus, moringa seeds and fava beans have all been used to help sediment water.
Click here to read more about different sedimentation methods.
Step 3 – Filtration
Filtration methods are ways to clean water and are commonly used after sedimentation to further reduce turbidity and remove pathogens. Filtration is a physical process which involves passing water through filter media.
Sand and ceramic are the most common filter media, although cloth and membranes can also be used. There are various types of filters that are used by households around the world.
* Cloth filter
* Biosand filter
* Kanchan arsenic filter
* Ceramic pot filter
* Ceramic candle filter
* Sawyer Filters
Click here to read more about each of these water filters.
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Step 4 – Disinfection
The next step in household water treatment is to remove or kill any remaining pathogens through disinfection, The most common methods used by households around the world to disinfect their drinking water are:
* Chlorine disinfection
* Solar disinfection (SODIS)
Turbid water helps pathogens to "hide" from chemical, SODIS and UV disinfection.
Reducing turbidity by sedimentation (see Step 2) and filtration (see Step 3) is necessary to improve the effectiveness of these disinfection methods.
Click here to read more about different methods of disinfecting water, including electrochlorination.
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Step 5 - Safe Water 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's 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 your 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 don't make each other sick.
The container should prevent hands, cups and dippers from touching the water, so that the water doesn't get recontaminated.
Click here to read more about safe water storage.
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