Pressure management is one of the most important Water Demand Management interventions that
can be implemented by a water utility in its efforts to reduce leakage. Since leakage is driven by
pressure, any efforts which result in the reduction of water pressure for even part of the day will
reduce the leakage to some extent. Despite the obvious benefits that can be derived through proper
pressure management, relatively few water utilities around the world are in fact implementing any form
of pressure control.
If implemented correctly, pressure management can be successful in reducing leakage from existing
and new burst pipes as well as reducing the hidden and often overlooked background leakage. In
certain circumstances, pressure management can also result in a significant reduction in the “normal”
consumption and will have the hidden benefit of extending the lifespan of the reticulation system. With
so many positive aspects to pressure management it is therefore surprising to find that many water
utilities around the world tend to shy away from such measures for a variety of reasons, most of which
are based on popular misconceptions. Virtually every water supply system which is operating on a full
24-hour pressurised supply has some scope for pressure management whether or not it is a flat area
or very hilly. The paper will provide additional information on the key issues to be considered when
contemplating the implementation of pressure management. It will also explain the basic concepts of
advanced pressure control where pressures are controlled using electronic or hydraulically operated
modulating devices which provide greater flexibility and this also greater savings.
Water supply systems worldwide are generally designed to provide water to consumers at some
agreed level of service which is often defined as a minimum level of pressure at the critical point which
is the point of lowest pressure in the system. In addition, there may be certain fire-flow requirements
which can over-ride the normal consumer requirements. The systems are designed to accommodate
these pressure and flow requirements during the period of peak demand which would normally occur
at some specific time of the day and during a particular month in the year. In other words, the systems
are designed to provide the appropriate supply during a very short period in the year and for the
remainder of the time the systems tend to operate at pressures significantly higher than required.
Even within the same system, there will be areas of high pressure due to topography and/or distance
from the supply point with the result that many parts of a supply area will operate at pressures
significantly higher than required in order to ensure that there is sufficient pressure at the one critical
point.
Managing water pressures in a supply area is not a simple issue and there are a great many items to
consider. The common factor in every system is the fact that leakage is driven by pressure and if the
pressure is increased, the leakage will also increase. Conversely, if the water pressure can be
reduced, even for part of the day, the leakage will also decrease. No two systems react in the same
manner to pressure and it is often very difficult to predict the reduction in leakage due to a decrease in
pressure with confidence. Many theories have been postulated to explain the pressure-leakage
relationships in a municipal water supply system and the most widely accepted theory is that of Fixed
and Variable Area Discharges (FAVAD) which was first suggested by John May from the UK water
industry in 1995 This theory is fully explained by May in his paper (May, 1994) and further details are
provided in the PRESMAC User Manual (WRC, 2001).