blog post

New Filter Gives Drinking Water a Silver Lining

A young girl in Pakistan's Sindh province lines up for clean drinking water provided by UKaid. Image via Department for International Development.

A young girl in Pakistan’s Sindh province lines up for clean drinking water provided by UKaid. Image via Department for International Development.

The next time that you go to your sink and pour a glass of water, take a second to think about what’s in it. It likely has a little bit of chlorine, some fluoride for your teeth, and small amounts of minerals—but most importantly it has no appreciable amount of nasty disease-causing pathogens or toxic heavy metals. If it did though, you could now use an inexpensive filtration device that employs silver nanoparticles, developed Dr. Thalappil Pradeep and his colleagues at the Indian Institute of Technology Madras.

It’s sometimes easy for us to forget that up to 11% of the world’s population does not have reliable access to clean drinking water. In many countries the water that is available to the poorer segments of their population is contaminated with bacteria and viruses or polluted with heavy metals such as arsenic, mercury and lead.

Even in America we have had some rather high profile incidents of water contamination making people sick, though not in the recent past. In developing countries, it can be cost prohibitive for individual households to filter and sanitize their own water. This is where Dr. Pradeep’s silver nanoparticle innovation comes in.

Silver has long been known to have anti-microbial properties and because of this it has been used in multiple consumer and medical products. When silver is brought down to the nano-scale it does a great job of killing harmful bacteria and viruses but can also be toxic to humans in sufficiently high concentrations. This has made many people shy away from using it as a method of water treatment, but Dr. Pradeep and his team have come up with a way of making filters that are able to release small, controlled amounts of silver ions—effectively killing harmful microbes in the water. They do this by building up a clay-like support structure using a mixture of aluminum and chitosan and then growing silver nanoparticles inside nano-sized cages of the claylike support. While the silver nanoparticles do the job of killing microbes, the clay-like support can be loaded with other materials such as manganese dioxide or iron to remove heavy metal contaminants such as lead and arsenic.

Dr. Pradeep's water filtration device. Reprinted with permission from his recent article in the Proceedings of the National Academy of Science.

Dr. Pradeep’s water filtration device. Reprinted with permission from his recent article in the Proceedings of the National Academy of Science.

This filter can be made without the use of any electricity and can filter 500 times the amount of water needed in its production. This makes the overall process of creating these filters much greener than that of traditional water filters which require a significant amount of energy to manufacture and have a fixed lifespan. After providing safe drinking water for over a year, Dr. Pradeep’s filters can be brought back to life with no sophisticated chemical treatments. They can simply be boiled to reactivate their silver-releasing power. These filters are also extremely affordable, coming in at an expected operating cost of fewer than three American dollars  a year for a family of five.

The end result is a reusable, affordable water filter that has the ability to be customized to the needs of people the world over. With so much attention being paid to the possible dangers of chemicals and nanomaterials entering our water it’s nice to see that people are also innovating ways of using them to help clean water for people who need it the most.