Solar distillation project wins UK Junior Water Prize 2025

30 June 2025

Growing up in rural India, where drinking water wasn’t always available, was the inspiration for the winner of this year’s competition

It was thinking back on her childhood in rural India that gave Divyasri Kothapalli the idea for the project that won her the UK Junior Water Prize (UKJWP) 2025 last month.

She was inspired to enter the competition, which is aimed at solving environmental challenges in water, following her brother’s involvement in last year’s prize. “My brother and I are extremely passionate about solving water-related challenges from a young age, due to our upbringing in rural India. Safe drinking water wasn’t always accessible,” says Divyasri, who is completing A levels in maths, further maths, economics and physics at St Paul’s Girls’ School in London.

“I wanted to explore a method that didn’t rely on electricity, was low in cost, and could realistically work in off-grid areas. I wanted to somehow use the fact that most of these areas have access to water and heat but are unable to safely use it.”

The result of those explorations – which Divyasri squeezed in around her regular schoolwork on evenings and weekends – is a solar still designed around a sealed heating chamber and a focusing lens. It works by boiling contaminated water in a repurposed cooking pot, with a beam of sunlight focused using a type of compact plastic lens known as a Fresnel lens; the resulting steam is collected in a glass jar connected to the pot with a silicone tube.

Divyasri Kothapalli, winner of this year's UK Junior Water Prize (UKJWP).

The design’s strength is in its simplicity. As Divyasri writes in her paper: “With no need for electricity or pumps or chemicals, and with readily-available components such as cooking pots, the model is adaptable to rural households or small community use.”

As currently designed, the solar still can produce only a small quantity of water but Divyasri’s paper includes options for potentially increasing output. And she points out in her paper that, “producing one to two litres per day from a few hours of sunlight could reduce reliance on unsafe water sources or firewood used for boiling”.

The UK Junior Water Prize jury, which was chaired by Renuka Gunasekara of Arcadis and included Peter Rook, CIWEM’s early careers president, commended Divyasri for identifying a specific research gap, namely how solar distillation could be adapted for low income, water scarce communities with limited infrastructure.

Divyasri wins a trip to Sweden this August to represent the UK at the Stockholm Junior Water Prize (SJWP) 2025, which will be held during World Water Week. She also wins a £500 cash prize and a year’s subscription to The Environment.

Each year SJWP attracts entries from around 35 nations, with HRH Crown Princess Victoria of Sweden awarding the prize to the winning student or group in a ceremony that features a flag parade. The UK round and Divyasri’s trip to Sweden are arranged by CIWEM in partnership with competition sponsors Jacobs and Arup. The winner receives a prize of USD$15,000. Last year’s winners were Christopher Whitfeld and Jonathan Zhao of the UK, for a project to remotely estimate the levels of PFAS – commonly known as ‘forever chemicals’ – in drinking water.

Divyasri is thrilled to have been selected: “It’s validating to know that something that is so rooted in my personal experience and focused on helping the less fortunate has been recognised at this level. It has also encouraged me to keep pushing the boundaries of what’s possible with simple and accessible technology.”

She is particularly looking forward to the trip to Stockholm because of the opportunity to “meet like-minded people passionate about solving water problems, share ideas and learn from new and diverse perspectives from around the world.”

Once she has completed her A levels, Divyasri hopes to study engineering at university and has an ambition to “start a business or non-profit organisation focused on providing solutions to water-related issues around the world”.

The UK runner up was a project to reduce the operation of storm overflows in the UK sewage system. William Jones and Jamie Markell of St Plumpton College, East Sussex and Collyer’s College, West Sussex designed a system to alert householders to times of peak flow, thereby enabling them to delay using household appliances to reduce the risk of storm overflows. The pair share a cash prize of £250, a year’s subscription to The Environment and a mentor session.

All UK Junior Water Prize entries, winning or not, are encouraged to develop their projects further. You can support them by contributing your time and expertise through CIWEM’s online mentoring sessions. If Divyasri’s or William and Jamie’s projects or any of the following short-listed topics sound of interest, please get in touch with awards@ciwem.org for more information on how you can contribute: 

• Multi-stage water purification using mechanical filtration, biofilm formation and electrochemical treatment for potability in low-infrastructure environments;
• UV-A technology to reduce the risk of illness resulting from exposure to bacteria during water sports;
• Methods for microplastic removal from the Thames, and how to move from a literature review to a practical experiment;
• Using AI to change how sustainable drainage systems impact combined sewer overflows.

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Jo Caird is editor of The Environment

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