A Conversation with Mark McEwen, General Manager for Capital Investment, Scottish Water
For over 160 years, the Loch Katrine gravity‑fed water system has quietly served as one of Scotland’s most remarkable engineering achievements. Built in the Victorian era and still providing high‑quality drinking water to more than a million people in Glasgow, it stands as a rare example of historic infrastructure that remains fundamental to modern life.
As part of CECA Scotland’s Projects that Built Scotland campaign, we spoke with Mark McEwen, General Manager for Capital Investment at Scottish Water, to explore the legacy, operation and future of this iconic system.
Q: For those unfamiliar, what is the Loch Katrine water system and why is it so significant?
Loch Katrine is a gravity‑fed water system and one of Scotland’s most historic pieces of public infrastructure. Developed in the mid‑19th century, it was designed to provide Glasgow with clean, reliable drinking water as the city expanded and public health challenges intensified. The first aqueduct was built from 1855 and opened by Queen Victoria in 1859. A second aqueduct followed, beginning construction in 1885 and coming into service in 1901 to meet growing demand.
Its significance lies in its ambition, the scale of the reservoir, the precision of the aqueducts and the Victorian commitment to public health. More than 160 years on, the system still forms a key part of Scotland’s water supply infrastructure, delivering high‑quality drinking water to over a million people without relying on pumps, a remarkable legacy of long‑term engineering vision.
Q: What were the conditions in Glasgow in the 19th century that made the scheme necessary?
Like many UK cities at the time, Glasgow’s population was rapidly increasing, and water supply was wholly inadequate both in volume and quality. Public health risks were high and wastewater disposal was another significant challenge. The arrival of Loch Katrine provided, for the first time, a reliable, clean, high‑quality supply into an expanding and increasingly dense urban area.
Q: From an engineering perspective, what stands out as the most remarkable aspect of the original system?
For me, it’s the fact that the entire system operates purely on gravity flowing from Loch Katrine all the way into Glasgow. The Victorians achieved an astonishing level of precision with very basic tools, constructing a 26‑mile aqueduct on a gradient of roughly one metre per six kilometres. That takes phenomenal accuracy.
The workforce built tunnels, open cuts and elevated sections across very challenging landscapes. When you consider the constraints they faced compared to modern technology, the achievement is staggering.
Q: How does the system actually work today?
The fundamentals haven’t changed at all. Water from the catchment flows into Loch Katrine and then into the aqueducts. From there, it travels towards Craigmaddie and Mugdock reservoirs, where it’s treated before being supplied into Glasgow. Around 110 million gallons a day pass through that process.
Although the basic principle is unchanged, we now have modern monitoring and control technologies layered onto the system.
Q: What makes a gravity‑fed system beneficial compared to pumped systems?
The key benefit is energy. If we didn’t have gravity doing the work, we’d be pumping around 110 million gallons every day into the city, which would come with a huge operational cost. The gravity system saves approximately £65 million in energy costs each year and avoids significant carbon impact.
Q: What does maintaining a 165‑year‑old water system look like in practice?
Both original aqueducts still operate as originally intended but they require continuous monitoring and inspection. We use internal visual inspections, drones, ROVs, and other remote technologies to understand their condition.
We’re looking for issues like spalling, rockfalls, infiltration, culvert failures and corrosion. Based on what we find, we plan interventions, repairing or replacing sections so the system maintains its structural integrity and continues to protect water quality.
Q: Scottish Water has invested significantly in the system in recent years. What work has taken place?
There’s been a range of projects. At Loch Katrine itself, we completed works on the dam to protect against undercutting caused by storm flows cutting out damaged areas and installing reinforcement and new concrete.
For the aqueducts, we have significant investment planned for the next regulatory period (SR27), with programmes ranging from £10–25 million.
Q: Loch Katrine sits in a highly sensitive natural environment. How do you safeguard that?
The catchment itself is relatively undisturbed, mainly farming, forestry and low‑key tourism so it enjoys natural protection. Loch Katrine is also an important visitor destination, home to the Loch Katrine Visitor Centre and the historic steamship Sir Walter Scott, helping people connect with the area’s engineering and environmental heritage.
We are working closely with Forestry and Land Scotland on large‑scale woodland management including plans for around 4,600 hectares of tree planting over the next eight to ten years. This brings significant carbon benefits and protects against runoff during heavy rainfall. We’re also looking to where we can restore degraded peatland in the area, helping it store water naturally and reduce sediment flow into the loch.
Q: With Scotland’s net zero ambitions, what role can gravity‑fed infrastructure play in the future?
It’s a really interesting question, because if you look at an example like Loch Katrine which was leading‑edge, innovative and hugely ambitious in its time it highlights how different modern treatment works have become. Today’s treatment facilities tend to be very complex, energy‑intensive solutions that rely heavily on pumping, both to bring water in and, in some cases, to move it through the processes.
That naturally raises the question of how we create assets with the lowest possible carbon impact. There is definitely something to be learned from our Victorian predecessors, whose gravity‑fed designs remain both effective and sustainable more than a century later. The concept of gravity‑fed systems isn’t unique to Loch Katrine, but the enduring success of this one shows the value of low‑carbon approaches and how solutions like gravity‑fed infrastructure may need to become the norm as we respond to the climate challenge.
Q: Finally, what lessons can modern infrastructure designers learn from Loch Katrine?
Victorian engineers set a very high bar. The fact that the fundamental assets, the dam and aqueducts, still function today is remarkable.
By contrast, many modern treatment works, while technologically advanced, won’t look the same 150 years from now. Loch Katrine reminds us of the value of long‑term thinking and resilient, robust design. Those principles are as relevant today as they were in the 1850s.
