Sunday, April 29, 2012

Sustainable Water Supply is Key to Urban Growth and Development

Nairobi is experiencing a water crisis of the kind that lures environmentalists into fits of gloomy Malthusian prognostications on demand and supply. For Nairobians, running taps and showers are almost luxuries of a past they remember with nostalgia.

The water situation in Nairobi is scourge on our national pride. It undermines the livability and attractiveness of the city. The nickname “The Green City in the Sun” now invites sniggers.

Less than 50% of Nairobi’s residents have direct access to piped water and only 40% have daily access to water. Only 22% of residents of the informal settlement, home to 60% of Nairobi’s residents, have access to piped water. Furthermore, Nairobi is insanitary; only 40% of Nairobi residents with access to the city’s water and sewerage network water-borne sewage.

The bulk of water supply for Nairobi comes via an old pipeline network from Ndakaini in Thika, Sasumua in the upper ridges of the Aberdares, Kikuyu springs and Ruiru in Kiambu. These sources are insufficient. The current demand for water exceeds supply by about 377,000 cubic meters per day. The supply deficit is exacerbated because 40-60% of the water destined for Nairobi is unaccounted for, lost.

The government, with funding from the French Development Agency and the World Bank undertook a study to identify new water resources within a radius of 70km of the Nairobi. The report, “Feasibility Study and Master Plan for Developing New Water Sources for Nairobi and Satellite Towns”, recommends groundwater development, abstraction and diversion of three rivers to supply additional water to the Thika reservoir by 2017.

Sadly, these new water resources will add a paltry 203,040 cubic meters per day, raising the supply to 685,980 cubic meters per day in 2017, against a projected daily demand of 1 million cubic meters. Moreover, additional diversions, abstractions and inter-basin transfers proposed between 2018 and 2030, but are unlikely to meet the projected conservative demand of 2.5 million cubic meters per day by 2030.

The solutions proposed in the feasibility study and master plan – increasing supply bulk volumes of portable water from outlying rural districts – were first developed and applied in Europe in the 19th century. Cutting and pasting solutions for Europe and North America from two centuries ago will not solve the problems of a dynamic Kenyan city.

Meeting urban water needs in the 21st century will require a paradigm shift. 19th century supply side solutions alone will not balance the ever-growing demand for water driven by rapid urbanization, shortage of surface and ground water due to climate change and competition from agriculture. Conventional approaches to urban water needs are unlikely to support sustainable communities and sustainable urban growth. The development of sustainable technologies and demand management measures are urgently needed.

Cities are hotspots of water consumption. But cities also have a huge potential to reduce their water footprint. Simple, low cost distributed innovations can deliver phenomenal reductions on urban water demand while creating new jobs in green plumbing and ecological engineering, improving environmental quality and creating exquisite habitat for urban flora and fauna.

I propose an approach that would reduce demand for centralized portable water through water use efficiency, reuse, recycling and purification of domestic wastewater, roof catchment and the abundant urban storm runoff.

Use of flush toilets (at 10-13 liters per flush) consumes nearly 40% of domestic water. Mandating the installation and use of low flush toilet would reduce water use per flush by 50%. Vacuum toilets use 0.5 liters of water per flush to transport the same volumes of human waste. Besides delivering outstanding water use efficiency, a dedicated vacuum sewer network connecting hundreds of households of can generate biogas as produce fertilizer for agricultural use. Furthermore, ecological sanitation approaches, which promote dry sanitation by separating solid and liquid human waste, offer low cost, low-tech non-polluting effective sanitation solutions for low-income urban households.  

Greywater – wastewater generated from showers, baths, hand basins, laundries and kitchens – is relatively easy to reuse. With minimal treatment, in the form of physical filtering and settling, greywater can be reused for toilet flushing and gardening. An ecological engineering approach through the application of constructed wetlands and wastewater aquaculture can be used effectively to for the treatment and purifying of wastewater and contaminated roof and urban storm runoff.

Water quality cascading, an approach that aims to match water quality to water use, is an important demand managing measure. Diversion of grey water from hand washbasin, washing machine and showering to toilet flushing is an example of water quality cascading.

Overall, national policy and institutional resources must focus on providing a framework for an integrated understanding of the multiple approaches to sustainable urban water and promote distributed, rather than centralized than water and sanitation strategies. Such decentralized infrastructure will play a vital role in water supply and demand while enhancing service quality and accountability.

1 comment:

  1. Hi Alex! Well said indeed! However we forget to think of the watershed and how water cascades and transitions from here to the end user. With this in mind, I want to advocate that in order for the city and its environs to have a sustainable supply, yes we will require innovative approaches in regards to greywater management, low flow toilets e.t.c. However the ultimate success lies in conserving the source of this water; the watersheds.
    Only then will we realize complete sustainability.Our organization is in the process of creating a model known as water funds in the Upper Tana watershed. You could think of it as a sort of trust fund where utility companies and large water users put funds into a kitty which are then re-directed to the watershed to facilitate conservation and incentivize the community to adopt better land management practices and alternative sources of income whose end goals are to preserve and conserve the green infrastructure in these watersheds.



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