The effect of pressure on leakage in water distribution systems

The results of pressure management field studies have shown that the leakage exponent is often considerably higher than the theoretical orifice value of 0.5. The purpose of this paper is to identify and analyse factors that may be responsible for the higher leakage exponents. Four factors are considered: leak hydraulics, pipe material behaviour, soil hydraulics and water demand. It is concluded that a significant proportion of background leakage can consist of transitional flow, and thus have a leakage coefficient value above 0.5 (although not above I). An important factor is pipe material behaviour: laboratory test results are presented to show that pipe material behaviour can explain the range of leakage exponents observed in the field. The complexity of the interaction between a leaking pipe and its surrounding soil is discussed and it is concluded that the relationship between pressure and leakage is unlikely to be linear. Finally, it is noted that if water demands are present in minimum night flows, the resulting leakage exponent is probably underestimating the true value.