| dc.description.abstract | Urban water supply utilities in developing countries are faced with challenges of low
service coverage and high unaccounted for water (UFW). UFW reduces the water
available to customers, and results in loss of revenue for the water utility. In Southern
Africa, UFW ranges from 11% to 60% and in Malawi it is between 28% and 48%.
Zomba has UFW of 30%. Most studies on UFW have not focussed on its partitioning into
real and apparent loss components. Crude UFW does not allow the water utility to
identify appropriate priority areas and actions for UFW reduction. It is against this
background that a study was carried out on the Zomba City water supply system to
partition UFW. The water supply system is owned and operated by Southern Region
Water Board (SRWB). The study analysed UFW, partitioned it into its components and
assessed major factors affecting the components. Four water supply zones (Airwing,
Malonje, Sadzi and Mtiya) were selected based on their unique characteristics. Historical
data on water production and consumption were used to assess overall UFW. Bulk meter
readings for each zone were taken for three months alongside the corresponding
consumptions. Flow and pressure loggers were installed to obtain Minimum Night Flows
(MNF) and assess pressures respectively. Water balances were carried out. Meter
inaccuracy tests were also carried out to assess the impact of meter errors on apparent
losses. Records of pipe bursts, faulty meters and queries on high bills were also used in
the study. The average UFW from 1999 to 2008 was estimated to be 27.5% of which real
losses represented 71% while apparent losses were 29%. The average UFW for the four
study zones was 13% for Airwing, 62% for Malonje, 51% for Sadzi and 6% for Mtiya.
Real losses in Airwing estimated at 73% of UFW, Malonje had 75%, Sadzi had 40% and
Mtiya had 23% as real losses. The remaining percentages represented apparent losses for
each study site. It was also established that real losses in Airwing were due to pipe bursts
mainly as a result of pipe age while in Malonje and Sadzi; the real losses were affected
by bursts due to pipe age and high pressures. It was found out that more than 58% of the
pipe network in the whole distribution system was over 60 years old. Malonje and Sadzi
areas had operational pressures above 50 m and experienced frequent pipe bursts. It was
also found out that 53% of customer meters tested were over 5 years old. Meter
inaccuracy tests also showed that all the meters under-registered and that 46% of the
meter errors were above the allowable tolerance of -5% at low flow rates and -2% at high
flow rates. It was concluded that the average unaccounted for water was above the 20%
recommended for Southern African urban water supplies. Partitioning of UFW showed
that different areas had different levels of real and apparent losses and gave a hint on
UFW components hence is an important tool towards proper planning of priority areas in
UFW control strategies. Real losses in Airwing were affected by distribution network
age, while in Malonje this was affected by pressure and distribution network age. Sadzi
had a high level of apparent losses as the number of connections in the zone was very
high. It is recommended that routine water audits be done for the other remaining areas to
come up with a comprehensive UFW control strategy. It is also recommended that
feasibility of pressure management for UFW reduction be investigated in Malonje area.
Distribution network replacement is recommended in Airwing. UFW control strategy for
Sadzi should focus more on reducing the high levels of apparent losses. | en_ZW |
