Treating water in a home or a building may be relevant in a few situations. First, in communities without sufficient capital to build water treatment facilities, residents are forced to drink bottled water. This happens thorughout the world, from the farmlands of East Africa to the rural communities of California. Second, many in the sustainability community advocate a return to more localized utility services for water or energy. As an example, advanced building designs such as the Omega Institute or the new San Francisco Public Utilities Commissions (SFPUC) building, are experimenting with on-site water management and wastewater treatment. While these buildings are models, most buildings that treat water on-site do so through necessity and face a host of regulatory hurdles. Point-of-Use (POU) treatments, which filter water through in-building systems or at the sink, are often regarded as unreliable by water system managers as the primary water safety technique. Understandably, regulatory agencies are reticent to endorse systems that place responsibilities for filtration system maintenance on residents, especially poor ones. When the alternative is buying bottled water, however, the issue becomes murkier.
A variety of physical and chemical point-of-use (POU) treatments exist1. The most prevalent treatment approach in homes is boiling water, with over 1.2 million people using it as a means for treatment. Boiling water can significant reduce the presence of bacteria (E.coli was seen to decrease by 98.5%), but its success depends on access to energy sources or wood and compliance.
Filtration technologies such as slow-sand biosand filters and ceramic filters effectively remove protozoa and bacteria. Biosand filters combine filtration and biological removal of contaminants in one device. Typically, the sand traps suspended solids and pathogens and a biolayer uses microbes to consume pathogens. Household ceramic filters typically filter water through a ceramic pot with small pores (down to 0.2 um) capable of filtering bacteria, protozoa, and are good for dealing with turbidity, iron, coliform, and E.coli. Filtration happens at approximate rates of 1-3 liters per hour and the filters generally cost between USD $5-25. The inside filter element should be replaced every 1-2 years and regularly recharged. While biosand and ceramic filters are relatively low-cost, they require maintenance and operation and do not provide residual protection, so filtered water may become contaminated in storage2.
Solar disinfection uses UV-A and heat to kill microbes, viruses, and protozoa. A common method of UV treatment is to put water of relatively low turbidity into a plastic bottle, shake it for oxygenation, and place it on a roof in the sun for several hours. Such treatment methods can cost only $0.63/person/year3. Alternatively, household UV treatments can use engineered solutions with different wavelengths to create relatively low-cost devices. Turbid water can be filtered beforehand, but UV and solar treatments may not provide residual protection, use power, and effectiveness depends on climate if not using energy-intensive bulbs.
Household chlorination using small bottles that are added to water supplies kills viruses and bacteria and also provides residual protection2. It is relatively inexpensive, ranging between $0.50 and $1.00/person/year. Chlorine typically requires 30 minutes of contact time to kill pathogens and can inactivate up to 99.99% of pathogens. Chlorine is an effective option but people have objected to its residual taste and odor for decades.
With each of the techniques, a combination of filtration and disinfection are likely the best approach to address all potential contaminants.
1. Sobesy, M. Managing Water in the Home: Accelerated Health Gains from Improved Water Supply. (World Health Organization: Geneva, Switzerland, 2002).
2. Lantagne, D., Quick, R. & Mintz, E. Household Water Treatment and Safe Storage Options in Developing Countries: A Review of Current Implementation Practices. (Woodrow Wilson Center: Washington, D.C., 2007).at <http://www.wilsoncenter.org/sites/default/files/WaterStoriesHousehold.pdf>
3. Clasen, T., Cairncross, S., Haller, L., Bartram, J. & Walker, D. Cost-effectiveness of water quality interventions for preventing diarrhoeal disease in developing countries. Journal of Water and Health 5, 599 (2007).