Climate & Cities
A City's Water Leaks Before It Reaches Anyone
A meaningful share of treated water never arrives at a tap, lost through ageing buried pipes that are expensive to find, expensive to reach and invisible until they fail.
Water networks lose a substantial volume between treatment and the tap. The losses are unglamorous, hard to locate and costly to fix, which is why they persist.
The network is old and buried
Distribution mains in established cities were laid over many decades in a range of materials, some of which corrode and some of which become brittle with age.
Joints move as the ground shifts with temperature, traffic loading and drying soils, and a joint that weeps rather than bursts can do so unnoticed for years.
Because the pipe is under a road, nothing about the surface indicates the condition of what lies beneath until water reaches the surface.
Finding leaks is a detection problem
Leaks are located by listening for the sound of escaping water, by monitoring flow into a district at night when legitimate use is low, and by pressure analysis.
Night flow that never falls to near zero indicates loss somewhere in that district, but narrowing it to a location still requires fieldwork street by street.
Some leaks never surface because the water finds a drain or a permeable layer, and those are the ones that run longest.
Pressure management reduces loss without excavation
The rate at which water escapes from a given hole depends on pressure, so lowering pressure at night reduces the volume lost across the whole network.
Lower pressure also reduces the stress that causes new bursts, so the benefit compounds over time rather than being a one-off saving.
The limit is that pressure must remain sufficient for the highest properties and for firefighting, which sets a floor below which management cannot go.
Replacement competes with everything else in the street
Renewing a main means excavation, traffic management, temporary supplies and reinstatement, and the reinstatement is often the largest single element.
Coordination with other utilities is difficult because each has its own asset plan, funding cycle and regulator, so the same street is frequently opened more than once.
Trenchless methods that line or replace pipes from a small number of pits reduce disruption but cannot be used everywhere, particularly around complex junctions.
Losses inside private property are a separate matter
The pipe from the main to the building is usually the property owner's responsibility, and a leak there is invisible to the network operator unless the property is metered.
Unmetered properties therefore have no signal that anything is wrong, and the loss continues until it appears at the surface or affects supply.
Metering programmes are justified partly on this basis, since detection at the boundary is what turns an unknown private loss into a fixable one.
Questions readers ask
Do green roofs save energy?
Modestly, and mostly on poorly insulated buildings. On a well-insulated roof the thermal effect is small. Run-off attenuation is the benefit that reliably justifies them.
Are green roofs maintenance free?
No. They need outlet clearance, occasional weeding and inspection, and they need access to do it. Most failed installations were neglected rather than badly built.
