When engineer Nancy Matheri relocated from Nairobi to Nakuru two decades ago, she was unprepared for the water quality challenges that awaited her.

Specialising in water and environmental engineering, Nancy recalls her first sip of Nakuru’s water as both “salty and hot,” leaving her uncomfortable.

As a young mother at the time, she noticed that many children around her had discoloured, brown teeth. Drawing from her professional background, she quickly identified the culprit ;fluoride. What shocked her, however, was the high concentration of said fluoride in the water.

“Back in the 1990s, boreholes in Nakuru were drilled up to 150 metres. Today, they go as deep as 350 metres. The deeper we drill in this volcanic region, the higher the mineralisation and that means more fluoride,” she explains.

According to the World Health Organization (WHO), the safe limit for fluoride in drinking water is 1.5 mg per litre. Yet, boreholes in Nakuru register concentrations ranging from 0.5 mg per litre to over 50 mg per litre, posing serious health risks.

She notes that prolonged consumption not only damages teeth but also weakens bones, as studies suggest.

Faced with this growing crisis, Nancy founded M&T Circular Sanitation Limited, a startup dedicated to affordable water and sanitation solutions.

Sample of the household fluoride filter showcased by Nancy Matheri during the National Research Festival at Egerton University on 18th August, 2025.

Photo credit: MUTHONI WANJIKU/MTAA WANGU

For the past two and a half years, she has been researching and developing a low-cost fluoride removal system using locally available materials.

Unlike existing market solutions that remain unaffordable for most households, her innovation is designed to be accessible. A basic household filter costs Sh 5,000 and can last for a full year.

“Every person needs four to five litres of clean water per day for cooking and drinking. This filter ensures families can meet that need without fluoride exposure,” she says.

Nancy notes that the startup offers different options: a 20-litre bucket filter for household use, an in-line system priced at Sh 10,000 for homes with piped water, and larger commercial units tailored for communities with boreholes.

"These systems can reduce fluoride from 10 mg per litre down to below the safe limit," she notes

Funded by Egerton University, which also provided production space, the project has now reached its final stages of commercialisation.

However, Nancy admits that like most startups, capital remains a hurdle.

“The university supported the research phase, but we are still waiting for funds to be disbursed for commercialisation. With startups, you’re always short of money,” she notes.

Her long-term vision is to protect future generations in Nakuru, Baringo, and Naivasha from the devastating effects of fluoride. Beyond physical health, she highlights the psychological toll.

“Children suffer from low self-esteem due to brown teeth. They lose teeth early, face restrictions in employment, and often feel different from their peers. It’s not just a health problem it’s a social problem too,” she highlights

Nancy urges young innovators to take advantage of the increasing availability of grants for youth-led ideas.

“There is money out there. Young people just need to be intentional and search for opportunities, fill out applications, and reach out for mentorship. No one will come looking for you at home; you must step out,” she concludes.

Water engineer finds solution for Nakuru's brown teeth menace

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Muthoni Wanjiku