Abstract
M.Phil. (Engineering Management)
The aim of this study was to determine the optimal point at which domestic water meters are to be replaced in order to minimize apparent water losses while ensuring efficient use of financial resources.
A literature review was undertaken to review the existing body of knowledge in relation to the accuracy of water meters, the effects of ageing on water meter accuracy, the impact of water meter inaccuracies on apparent water losses, as well as water meter replacement strategies.
A water meter management database was analysed using the relative meter error method to determine if a relationship exists between domestic water meter age, total registered volume and accuracy. The volume of apparent water losses caused by inaccuracies due to domestic water meter age and total registered volume was determined. The net present value chain (NPVCn) method was used to determine the optimal domestic water meter replacement period.
This study found no absolute relation between water meter age and total registered volume. This is probably the reason why several authors and water boards suggest a meter lifespan either by age or total registered volume and not both. A relationship was found to exist between water meter age and accuracy as well as between total registered volume and accuracy. The trend line of the median relative meter error moved from over-registration to under-registration as water meter age increased. The trend line of the median relative meter error decreased was however found to increase from under-registration to over-registration as the total registered volume increased.
The average volume of apparent losses due to meter inaccuracies was determined to be 1.8 kl per meter/per month. This figure, when considering the number of meters in the municipality, amounted to 2.8% of the municipality’s total system input volume and 7.8% of the non-revenue water.
The optimal water meter replacement period of the municipality was determined using the NPVCn method to be at 9, 12 and 16 years and total registered volumes of 3 971, 5 162 and 6 750 kl at 10%, 8% and 6% real discount rates, respectively.