Providing clean water to the developing world
Household water treatment offers the best hope for nearly 900 million people.
by Michael D. Robeson
Many Americans take clean drinking water for granted. However, much of the developing world is still grappling with the challenges of supplying water that is safe for human consumption. The problem affects nearly 900 million people around the globe and leads to 2.2 million deaths by waterborne diseases annually. More than half of the victims are under the age of six.
While the danger in urban areas stems from aging or inadequate water treatment infrastructure, the risk is most acute in rural communities lacking the density or the resources to build and support water treatment facilities.
Many rural residents still fetch water from rivers, lakes, ponds and streams contaminated with human and animal waste, whether from open defecation or factors such as seepage from septic tanks and pit latrines. Even people with access to cleaner water from common wells, collected rainwater or centralized taps face the risk of pollution by an unsanitary container or improper storage in the home.
For these reasons, groups such as UNICEF and the World Health Organization (WHO) have long recognized that the most practical immediate strategy for improving rural drinking water quality is to provide solutions for treating and safely storing water at the household level.
The upshot has been the development of a variety of household water treatment and safe storage (HWTS) technologies designed to improve water quality at the point-of-use (POU), as well as the publication of WHO specifications for evaluating the microbiological performance of different HWTS systems in 2011. That 2011 WHO document was the first to establish target performance levels for bacteria, virus and protozoa in POU water treatment, providing a benchmark for measuring the relative effectiveness of each technology option.
From chlorination to filtration
One common POU solution involves chlorination — essentially the same treatment used to disinfect public water supplies in the early 1900s. The most widely adopted model in this scenario was developed by the Centers for Disease Control and Prevention (CDC) and the Pan American Health Organization in response to a 1990s cholera epidemic in South America. Under this model, diluted sodium hypochlorite is manufactured locally, bottled and added to water by the capful for disinfection. Users agitate the water and wait 30 minutes before drinking.
Benefits of this approach include low cost per treatment and proven reduction of most bacteria and viruses. Drawbacks include relatively low protection against parasites such as Cryptosporidium, potentially objectionable taste and odor, lower effectiveness in turbid waters and the need for a reliable supply chain as well as the financial resources to continually replenish the chlorine-bleach solution.
An alternative household water treatment is solar disinfection. Initiated by the Swiss Federal Institute for Environmental Science and Technology in 1991, this strategy requires users to fill plastic soda bottles with low-turbidity water, shake them for oxygenation and place them on a roof or rack for six hours in sunny weather or two days in cloudy conditions. Ultraviolet (UV) light from the sun works in conjunction with increased temperature to improve water quality.
The pros include ease of use, virtually no cost and effective pathogen reduction. The cons include the need to pretreat even slightly turbid water, long treatment times, especially in cloudy weather, the need for a large supply of clean bottles and the limited volume of water that can be treated at one time.
Most other POU options involve some form of filtration designed to remove pathogens by passing water through porous stones and a variety of other natural materials.
Multiple filter varieties
Clay-based ceramic filters, for example, remove bacteria through micropores in the clay and other materials such as sawdust or wheat flour that are added to improve porosity. The best-known design in this category is a flowerpot-shaped device by the nonprofit organization Potters for Peace that holds eight to 10 liters of water and sits inside a 20- to 30-liter plastic or ceramic receptacle, which stores the filtered water. Some ceramic filters are also coated with colloidal silver to ensure complete bacteria removal and prevent growth of the bacteria within the filter itself.
Slow sand filters, on the other hand, remove pathogens and suspended solids through layers of sand and gravel. One common household biosand filter consists of a concrete container incorporating layers of large gravel, small gravel and clean medium-grade sand. Prior to use, users fill the filter with water every day for two to three weeks until a bioactive layer resembling dirt grows on the surface of the sand. Microorganisms in the bioactive layer consume disease-causing viruses, bacteria and parasites, while the sand traps organic matter and particles.
As with chlorination and solar disinfection, both varieties have virtues as well as limitations. Ceramic filters are effective against bacteria and protozoa but not as effective against viruses, are breakable, typically last only two years, require as often as weekly cleaning and have a flow rate of only one to three liters of water per hour. Slow sand filters have a flow rate of 30 liters of water per hour — enough to suit a family’s needs — but again, lack adequate virus reduction abilities, are costly and difficult to transport at 170 lbs. and require periodic agitation and regrowth of the biolayer that can reduce filter efficiency if done improperly.
Both ceramic and slow sand filters also lack residual protection for filtered water, such as that provided by chlorine, raising the risk of recontamination unless a disinfectant is added after treatment.
A third option is a hybrid of the ceramic and sand designs. This approach utilizes porous ceramic particles blended with silver, zinc and copper, and deploys them in a layered configuration similar to slow sand filtration solutions. The filter is delivered in a barrel-shaped device with a strainer that filters out large debris, a ceramic/metal layer that neutralizes harmful microorganisms through an ion exchange process made possible by the unique properties of the clay itself and a built-in storage chamber for up to 18 liters of clean water.
Advantages consist of validated effectiveness in bacteria, protozoa and virus disinfection including industry-first compliance with WHO’s new household water treatment specifications, ion-based residual disinfection that keeps filtered water safe, minimal maintenance and a 10-year lifespan with no added costs for post-filtering chemical treatment or filtration media replacement, keeping costs low over the life of the filter. Downsides include a higher initial cost compared to other products and difficulty in outsourcing fabrication to developing world factories because the unique filtration materials are not locally available.
While household water treatment technologies for developing countries are not new, adoption still falls woefully short of need. According to the CDC, over two million people in 28 developing countries now use solar disinfection for daily drinking water treatment; however, that pales in comparison to the 900 million people who lack access to safe drinking water. Likewise, Potters for Peace has distributed over 200,000 ceramic filters in Cambodia and many more in other countries, but this only scratches the surface of a public health problem killing the equivalent of the entire population of Houston every year.
One stumbling block is the need to work through disparate non-retail channels to reach communities in need. Partnerships must be created with different nongovernmental agencies (NGOs) and multiple local organizations in each country. Finding willing partners is difficult, as is developing sustainable financial models for projects requiring donor funding and subsidies.
Therefore, distribution strategies vary widely. In the case of chlorination, implementations range from a faith-based group in northern Haiti making and bottling its own hypochlorite solution to a large-scale program in which NGO Population Services International both promotes and distributes its own product on a country-by-country basis through local channels such as community health workers and private pharmacies. In the case of ceramic filters, Potters for Peace helps local communities set up filter-making factories that in turn sell their products to NGOs. Each solution and supplier must forge its own path.
Equally challenging is the need to select the most appropriate treatment method for a community’s specific circumstances. Variables such as existing water and sanitation conditions, water quality, cultural acceptability, implementation feasibility and availability of a supply chain for refills or replacement parts will affect the decision. In addition, any implementation must include an education component to teach the use of each technology as well as proper sanitation, food and water handling.
Nevertheless, household water treatment holds the potential to save millions of lives. Until universal access to piped treated water is available, if ever, these decentralized technologies and the small-scale humanitarian models required to deploy them are the best hope for reducing the disease and death toll related to dirty water. Creative solutions, entrepreneurship and new business models will be needed to remove distribution obstacles, provide government funding or microfinancing and bring relief to millions of people who put their lives in danger simply by taking a drink.
Source: Water Technology.