Installing reverse osmosis (RO) systems alone at home is not a guarantee for safe drinking water, a recent study has found. While the technology has been proven capable of removing microbes under ideal operating conditions, a field level study in Chennai showed that microbial contamination was detected in samples from RO units, highlighting the lack of regular maintenance and filter replacement as key issues.

The results of the study ‘Evaluating Household Reverse Osmosis Systems for Microbial Safety: A Case Study from Chennai, India’ were recently published in the peer-reviewed Journal of Exposure Science & Environmental Epidemiology. The researchers Suzan Kagan et al, aimed at assessing the microbial safety of drinking water before and after household RO treatment to understand how education and awareness influence household water and maintenance practices. The survey conducted in Chennai covered 262 water samples from 216 households, looking at both treated and source water to assess the effectiveness of household water treatment systems.

The authors wrote that while RO systems reduce contamination, 31% of post-RO samples still contained Escherichia coli (E. coli), compared to 71% in untreated water. Furthermore, education levels were found to influence outcomes: 36% of post-RO samples from postgraduate respondents contained E. coli, versus 83% among those with lower education levels. They pointed out that RO systems reduced contamination, but offer limited protection without maintenance.

E. coli is a group of bacteria that normally live in the intestines, but certain strains of it can produce toxins that cause severe food poisoning, diarrhoea, and vomiting. Another paper published in Scientific Reports in 2025, by Shohaib Mustafa et al, on ‘Household Adoption of Domestic Water Filtration for Combating Waterborne Diseases in Developing Countries’ recorded the fact that contaminated water was one of the leading causes of several waterborne diseases, such as typhoid fever, cholera, giardiasis, dysentery, hepatitis A, and Salmonella infection, and domestic water filtration was seen as a way to counter the consumption of contaminated water from unsafe sources.

The study also posited an interesting correlation that was observed between education level and the presence of E. coli in drinking water. For respondents with postgraduate degrees, 36% reported an incidence of E. coli contamination in their drinking water, while for non-educated respondents, this value increased to 83%. Many households assumed that once an RO machine was installed, no further vigilance was needed, which led to complacency about cleaning and servicing, and created a gap between perceived and actual safety.

This highlights the critical role of user knowledge, practices, and proper water handling in preventing contamination, particularly in households using RO systems, according to the authors. Interestingly, the results of the 2025 study by Mustafa et al revealed that awareness of risks associated with contaminated water, social influence, and water pollution knowledge are the most significant predictors behind the use of domestic water filtration plants, whereas cost is a potential barrier.

In the Chennai study, the authors argue that utilising only RO devices as a stand-alone solution to urban drinking water safety may not be effective, and may worsen inequalities, because low- and middle-income households often buy systems with great difficulty and then realise they cannot afford to maintain them. What is required is a chain of quality and hygienic water supply, beginning with reliable piped supply, regulation of point-of-use devices, education on maintenance and hygiene, and servicing structures that are affordable.