Variable speed drives can help address one of the most persistent challenges facing water networks, says Torben Poulsen and James Chalmers, ABB.
Water scarcity is far from a distant concern.
Approximately one in four people globally lack access to safe drinking water, and four billion face severe shortages for at least one month each year.
What makes this harder to accept is that a significant share of treated, potable water never reaches an end user at all – lost instead through leaking distribution networks before it can get to the people who need it.
With population growth and increasingly unpredictable weather patterns placing mounting pressure on available supply, leakage is a problem that water utilities cannot afford to overlook.
The pressure behind the problem
Network leakage is rarely the product of a single catastrophic event. In most cases, it results from the sustained, cumulative stress that over-pressurisation places on infrastructure – stress that adds up quietly over time until it manifests as burst pipes, joint failures, or chronic low-level seepage.
The primary form this over-pressurisation takes is the pressure transient: a shockwave that travels through a pipe network each time a pump is started or stopped using a direct-on-line (DOL) starter.
Without any form of ramp-up control, a DOL-started pump reaches full operating speed almost instantly, and the resulting hydraulic surge exploits any vulnerability in the network it passes through.
Transient pressures under these conditions can reach double the network’s design tolerance. When a pipe bursts at the surface, the consequences are visible. Far more damaging, however, are the slow, undetected leaks that develop at weaker points and drain networks silently over time.
The operational consequences quickly accumulate. Each burst event draws on leakage detection resources, repair materials and workforce capacity, diverting these from other priorities and disrupting supply to communities in the process.
Even transients that stop short of causing a burst still put stress on every fitting, joint, valve and bend in the network, accelerating wear across the board.
This creates a damaging cycle that is difficult to break. When sustained low-level leakage reduces apparent network output, the typical response is to raise system pressure in an effort to maintain supply.
This instinct is understandable, but counterproductive. Higher pressure intensifies the very stress regime that caused the leakage in the first place. The cycle continues until infrastructure fails at a faster rate than it can reasonably be repaired.
But the consequences extend further still. Pressure surges in ageing pipe networks dislodge rust and sediment, introducing discoloration into the water supply – a visible quality problem that is difficult to justify to the public and harder still to remediate without addressing its root cause.
Changing the equation
Variable speed drives (VSDs) offer a technically and commercially proven response to the pressure management challenge.
They continuously adjust motor output to match real-time demand, rather than operating pumps at fixed speed regardless of what the network requires.
During periods of peak consumption, pump speed increases accordingly. As demand falls – typically overnight – the drive reduces speed while maintaining the target pressure setpoint.
The result is a network held consistently within its design parameters, without the pressure peaks and troughs that DOL control produces at every start and stop cycle. Every downstream component, from pipes and valves to seals and fittings, benefits from a more stable hydraulic environment.
VSDs also deliver significant reductions in energy usage. Pumping systems account for a large share of energy use across water distribution networks, and the relationship between motor speed and power draw means that even modest reductions in running speed produce efficiency gains.
When leakage is brought under control, operators stop bearing the ongoing costs of detecting and repairing it – freeing up budget that can be redirected towards broader network improvement.
It is worth noting that infrastructure replacement alone does not resolve the underlying problem.
Where the pressure regime responsible for pipe damage remains unchanged, newly installed pipework simply inherits the same stress conditions as its predecessor. Effective leakage reduction requires both control infrastructure and physical infrastructure to be addressed in parallel.
Delay has a price
The gap between what the technology can deliver and how widely it is actually being deployed is narrowing too slowly. For utilities facing tightening supply and ageing infrastructure, the case for VSD investment is well established; the more pressing concern is how much preventable damage accumulates while adoption lags.
Pipe assets typically remain in service for between 50 and 100 years, so the decisions made during installation or refurbishment carry consequences that extend well beyond any short-term operational cycle.
Embedding appropriate pressure control from the outset is smart long-term asset management – and the pressure of global water scarcity makes that case stronger with every passing year.
