Mark Sobsey

Mark Sobsey
Low-Cost Bacterial Water Tests

What are Low-Cost Bacterial Water Tests?

Simple, Accessible, Affordable Tests to Assess Microbial Water Quality and Safety in the Developing and Developed World

Worldwide, an estimated 1.6 million people die every year from diarrheal diseases attributable to unsafe drinking water, lack of sanitation, and poor hygiene; 90% of these are children under 5. In many developing countries, is common practice to dump untreated sewage into the same lakes, rivers, and streams that people use for drinking, washing, and bathing. Not surprisingly, fecal contamination is responsible for some 80 percent of all infectious diseases in the world. While long-term solutions to these problems will eventually require interventions to improve water quality and enhance sanitation infrastructure, much could be gained now through more frequent and widespread water testing.


In developing countries and other resource limited settings (such as after natural disasters), drinking and other water is almost never tested to estimate its risks of causing infectious diarrhea, enteric fever, cholera, and other life-threatening waterborne diseases. This is because there do not exist any simple, accessible, affordable, laboratory-independent methods to detect and quantify fecal bacteria in water used for drinking or other beneficial purposes. The portable tests that are available either do not give quantitative results, are not designed for populations to self-test, and/or are priced beyond what people can afford. (Even a test that costs $10, which may seem economically feasible for someone in the developed world, is cost-prohibitive for someone living below the poverty line.) As a result, the majority of people on the planet are drinking water about which they know nothing in terms of its fecal contamination, and millions continue to get sick and die unnecessarily from unsafe water.



While microbiologists have long thought about the idea of working on a simple, low-cost, accessible test for detecting fecal contamination in water, only recently has attention focused on developing such a test for remote communities and resource-poor settings.

“The development and deployment of an every-person’s test—simple, self-contained, portable, stable, and devised to not need electricity, refrigeration, or freezing—to determine water safety could be key for catalyzing global efforts to curb preventable illness and death due to waterborne fecal pathogens” —Mark Sobsey, PhD, Environmental Health Microbiologist
Dr. Sobsey has developed three versions of a simple, low-cost test for quantifying fecal contamination in water. Each variation involves a plastic bag into which is placed a water sample and a bacteriological medium that does not need to be boiled or autoclaved, and that can be incubated at temperatures 25–45 degrees Celsius—a range encompassing the environments of nearly all tropical and subtropical countries. The bag incubates overnight (on a shelf in someone’s home, for example) to give time for the bacteria to grow. The sample is then examined for evidence of bacterial growth. In one version, the plastic bag is divided into compartments that mimic test tubes, and bacterial density is estimated by the number of chambers that show characteristic color change and cloudiness. In the other two test versions, distinct bacteria colonies appear in a gelled medium or on an absorbent pad and can be counted directly. For each test, the estimated bacterial density can be compared to WHO Guidelines for safe drinking water. If bacteria are present at unsafe levels, users can determine whether to treat the contaminated water or find an alternative water source.


The strategic and rapid deployment of water testing could be a powerful tool for identifying safe water sources, directing water treatment efforts to high-risk communities, as well as for protecting populations from unsafe sources during natural disasters and emergencies. Dr. Sobsey envisions a future where water-related illness is substantially reduced by the widespread availability of a simple, low-cost water test.

“Household-level diagnostic testing is already done for tuberculosis, HIV/AIDS, malaria, intestinal parasites, diabetes, etc. There’s no reason why a simple, low-cost water test couldn’t be added for something as fundamental as safe water. In fact, new WHO guidelines for drinking water quality really encourage that water be tested on a regular basis for water management and for verifying quality.” —Mark Sobsey, PhD, Environmental Health Microbiologist
The next steps in the development of these tests are to finalize the design of the plastic bags with input from industrial designers and materials scientists, finalize the formulation of the bacteriological medium, and find companies that can produce these at very low cost. The current cost for the prototype, using materials purchased at U.S. retail prices, is between $1.25 and $2.25, depending which fecal bacteria are being detected. Dr. Sobsey believes the final cost will be well under $1, and possibly even as low as 10 cents.
“The current situation of no suitable tests for fecal bacteria in water is both intolerable and unnecessary. The small price to pay for knowing the safety of drinking water could reap enormous benefits in terms of improved health, increased productivity, and better quality of life.” —Mark Sobsey, PhD, Environmental Health Microbiologist