Even among water experts, most people are unaware that Windhoek is the "cradle of potable water reuse", being the very first city in the world to process drinking water from wastewater already in 1968 (long before Singapore, California et al.). Windhoek’s annual precipitation amounts to 370 mm coupled with an evaporation of 3400 mm. During drought periods, there is extreme water scarcity. The water deficit is growing due to increasing water demand and decreasing availability of raw water. During normal supply periods 75 % of raw water is abstracted from surface water. Yet, during the heavy drought period in 2017, less than 3 % of the water demand could be supplied from surface water. Industries had to shut down and private consumers were forced to cut their water consumption by > 50 %.
Under the BMBF research project "IWRM South Africa, MOSA " a new water resources modelling concept has been developed, consisting of three elements: (I) the water resources module (II) the water utilisation module and (III) the water intervention module. The Windhoek water map was developed to provide a detailed yet comprehensive overview of (I) the data and flows of available water resources, (II) the demand and development of water utilisations with different consumer groups and (III) the existing water infrastructure with a listing of which interventions (= technical as well as institutional measures) are possible to improve and secure water supply, to protect the water resources and the environment.
For Windhoek the most important intervention measures are: (1) continuous efforts to further improve the network and reduce water leakage and administrative losses, (2) institutional measures of water demand management, especially peak tariffs and fair, justified rules how to cut consumption during severe drought periods, (3) the development of the local aquifer as seasonal groundwater storage (with additional wells for groundwater recharge during wet periods and groundwater abstraction during dry periods) and technical measures, which are (4) long term investments like the import of water from the Okavango river basin (800 km in the North) and desalinated seawater from the coast (350 km away and 1.700 geodetic pump-meters below). Possible to realise within short time and financial limits was (A) the new wastewater treatment plant UJAMS to purify contaminated industrial wastewaters for non-potable reuse and is (B) the rehabilitation, upgrade and extension of the wastewater treatment plant GAMMAMS to produce raw water for further treatment in potable water production plants.
Ad A: The wastewater plant UJAMS has been operating successfully for four years and is one of the few high-tech plants in Africa well-functioning under sustainable public governance and professional operations. The plant development from design, procurement, contracting, technical pilot tests, plant construction and operations are explained. Figures are provided for plant components such as fine screen, membrane bioreactor and UV-disinfection. Future needs for further extension and long term solutions for sludge utilisation are outlined.
Ad B: The most urgent investment-project currently under preparation is the extension of the Gammams wastewater reclamation plant, producing raw water to be further purified in the New Goreangab potable-water production plant. Gammams needs to be rehabilitated, extended and modernised with an investment of roughly Mio 40 EUR. Initially the project was planned to be realised under an EPC (engineering, procurement, construction) through the municipality. Yet, being aware of the technological and financial risks and eager to create fair competition on a life-cycle-cost-basis (incorporating investment plus operational costs), the City has decided to go for a DBO (design, build, operate) model. Specific solutions for the open-technology tendering and the financial model are presented and explained.