Performance-based contract for nrw reduction and control strategy. A Bahamas success story

The purpose of this article is to present the context, preparation and implementation progress of the Bahamas Water and Sewerage Corporation’s (WSC) and Miya Performance-based Contract (PBC) for Non- Revenue Water (NRW) management in New Providence, Bahamas. This innovative contract was implemented as part of the IDB Loan Project: WSC Support Program. New Providence Water Supply and Sanitation Systems Upgrade.

Specialists from all international organizations, and managers and policymakers will gain an in-depth look into how this project was formulated, and how it was, and still is, being implemented and monitored. They can also gain lessons of experience on NRW and the use of PBCs from the experience of the Bahamas.

Background

In 2012, The Bahamas Water & Sewerage Corporation (WSC) contracted Miya to conduct a 10-year NRW reduction project. As a part of this contract, Miya Bahamas was required to reduce Non-Revenue Water (NRW) in the New Providence distribution system from 6.87 MIG/d to an annual average of 2.5 MIG/d by year 5 and to 2 MIG/d by year 7.

The island of New Providence, on which this program is centered, accounts for approximately 70% of the population of The Bahamas (351,000 inhabitants). The availability of renewable freshwater per capita in the country, and on this island, is one of the lowest in Latin America and the Caribbean. For this reason, the island population relies on groundwater and desalination as its only two drinking water sources. Groundwater, however, is very limited and over-abstraction is a serious concern. The well fields in New Providence had a maximum estimated capacity of 1.5 MIG/d, while customers’ demand fluctuates around 10 MIG/d. For this reason, over 90% of the drinking water supplied to the island comes from reverse osmosis plants, which yield a comparatively expensive product. In this context, the wáter losses in the distribution network, estimated to be close to 50% of the water produced, were considered economically and financially unacceptable. These losses originated from leaks in the network, unauthorized consumption, and metering inaccuracies.

Performance

The Baseline Survey Report showed that theBaseline of NRW in New Providence in 2011 was 6.87 MIG/d at an annual average system pressure of 24.6 psi and with an N1 pressure-leakage exponent of 0.9. The leakage exponent (N1) shows the interdependency of leakage on pressure. N1 values have been typically found to range from 0.5 to 2.5, depending on pipe material and level of leakage. Miya designed an NRW Reduction Strategy to ensure that all contractual conditions are met, starting from this baseline level. The NRW reduction strategy was designed to meet and maintain the NRW target level of 2.5 MIG/d at an annual average pressure of 25 psi by 2018, and to further reduce and maintain the NRW target level of 2.0 MIG/d by 2019, and maintain this level until 2022.

Mario Tavera, Project Manager de Miya Bahamas

Published in: FuturENVIRO Nº 69 AprilMay 2020