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By Thomas Kingsley, Publishing Associate: Researcher and Writer at Save the Water™ | August 11, 2026
Edited by Jaslene Szeto, Publishing Associate: Editor at Save the Water™
In some places, people do not always have access to clean water, so they store drinking water in buckets. For example, many rural areas in South Africa will deliver water in tanks during shortages. Residents then take this water home and keep it in buckets for their daily use. The problem is that water stored this way can develop biofilms, making it unsafe to drink. Researchers at the University of South Africa are studying how light can help kill bacteria in stored water..
Stored water can be dangerous because it does not move. Like still pond water, water in storage containers can allow microbes to build up on the surface as there is nothing to disturb the water and break them up. This creates a sticky layer called a biofilm. While biofilms are not always a bad thing, in this case, they provide a home for bacteria to multiply. They also make disinfectants like chlorine less effective.
Photoinactivation uses light to help stop bacteria from growing. The light helps special molecules make oxygen particles that can damage bacteria. These oxygen particles can hurt important parts of bacteria, such as their cell walls. This damage can kill harmful bacteria.
The researchers studied S. aureus, a type of bacteria commonly found in stored household water and responsible for a variety of illnesses. Some types of this bacteria are resistant to medicine. Therefore, photoinactivation may be another way to fight the bacteria without the use of antibiotics.
The researchers tested different materials and found that one made with orange peel extract helped the light treatment work better. When used to inactivate S. aureus, the best performer was able to complete it in fifteen minutes. When part of a biofilm, the same treatment worked in twenty minutes.. This is important because biofilms protect bacteria and make them harder to kill.
In the original tests, the photosensitizers, substances that use light to kill bacteria, could float freely in the water. The researchers also tested if the materials would still work when they were fixed in one place. In this second scenario, while they were not as effective, the best performing photosensitizer was still able to achieve almost complete inactivation after thirty minutes of light exposure. This was not perfect, but it was still a good result. In the future, these materials could coat water tanks to stop biofilms from forming and help keep water safer.
The researchers point out that their work shows promise, but it is still new. The general mechanism of photoinactivation was effective at treating biofilm, but it is not ready for practical use yet. Scientists need to do more research before this method can be used in real water storage systems.
Save the Water™ is a 501 (c)(3) non-profit organization with a mission to conduct research to identify and remove harmful contaminants in water and to raise public awareness about water contamination and its health impacts.
