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Coming clean on wastewater irrigation

Water scarcity is making agriculture increasingly dependent on re-use of wastewater (World Bank/Eric Miller)
Water scarcity is making agriculture increasingly dependent on re-use of wastewater
World Bank/Eric Miller

With their dense load of human waste, sometimes complemented by industrial effluent, the urban watercourses of the developing world could be seen as the embodiment of stench and disease. But for millions of urban farmers, they are also an invaluable asset. Urban agriculture produces an estimated 20 per cent of the global food supply and half of this is grown using wastewater, according to a recent 53-city survey by the International Water Management Institute (IWMI).

Vegetables and cereals, particularly rice, are the most common crops to benefit from nutrient-rich wastewater, but health risks, including cholera outbreaks, have led many city authorities to ban the practice. In reality, urban poverty and food shortages have tended to mean that irrigation with wastewater is unofficially tolerated. But at a global level, use of wastewater is now coming under the spotlight, as something which must be addressed, not ignored. At the 2008 World Water Week held in Stockholm in August, key players from the fields of health, water and agriculture offered New Agriculturist their points of view.

Waste not, want not

Given water scarcity issues and the potential impact of climate change, available water is going to be less and less, and therefore we will need to look at unconventional sources and uses of water. And among them is, of course, treatment and utilisation of wastewater.
Vahid Alavian, water advisor, World Bank

As a government, we would change the term 'waste' to 'resource', by using this so-called wastewater for agricultural purposes, and specifically urban agriculture. Because we realise that it is water which has a lot of nutrients, and at the same time our soils are degraded, so we can use it to improve on the yields in agriculture, and at the same time sanitise our urban centres.
Hon. Namuyanga Byakatonda, Minister of State for Water, Uganda

Wastewater irrigation is important because in the not too distant future it is going to become very much more common than it is now, out of necessity. By 2050 we're going to have 4 billion people living in water-scarce countries; basically it is going to be fresh water for the cities, wastewater for agriculture.
Prof Duncan Mara, School of Civil Engineering, Leeds University

Farmers and consumers are at risk from irrigation with contaminated water (©FAO/G Napolitano)
Farmers and consumers are at risk from irrigation with contaminated water
©FAO/G Napolitano

The main benefit of using wastewater is, of course, that of securing and improving livelihoods for farmers who use it as a source of water and nutrients in their agriculture. But there are also additional benefits: easier access to some of the horticultural products for growing urban populations and protection of downstream communities from the environmental and health impact of wastewater being dumped into rivers straight away.
Robert Bos, Water, Sanitation, Hygiene and Health programme, World Health Organisation (WHO)

Under water scarcity conditions, treated wastewater reuse is recognised by FAO as a resource that can be captured for irrigated agriculture and prevents coastal and inland watercourse degradation. The reuse of wastewater for agriculture is mainly applied by urban resource-poor farmers as a means to generate income by growing food. With recent soaring food prices, increasing costs of food supply and distribution to urban areas, food is less accessible to the poorer sectors of the population. FAO advocates and promotes urban and peri-urban agriculture as a key area of agricultural policy and sustainable development.
Sasha Koo-Oshima, water quality and environment officer, FAO, Rome

The right course of treatment

Treatment of irrigation water is important, and can be realistically done if we have a well planned out strategy. We do a quality monitoring of the wastewater, treat it as required and then release it for irrigation purposes. In water-scarce areas this could be an extremely efficient means, although if there is an abundance of water it might not be cost effective. So how you deal with wastewater will differ from place to place.
Nandita Singh, research scientist, Royal Institute of Technology, Stockholm

Quite often technologies are pushed which allow someone, at some level, to skim off a certain amount. Sewage treatment plants are huge, complex things. Even small things that would be used in the slums like septic tanks need manufacturing, need lots of compliance laws, etc. There are endless possibilities for installers, contractors and low-level bureaucrats to siphon off a little bit of money. So we always recommend that you use whatever is the simplest possible technology at any place.
Manoj Nadkarni, communication coordinator, Water Integrity Network

Treatment and utilisation of wastewater is one of the major options that many of our client countries will have to go to. In some cases one would have to look at large scale, tertiary treatment. In some cases it may be possible to look at community or even neighbourhood treatment facilities, depending on the situation. But it depends on what the government would borrow for and is prepared to invest in.
Vahid Alavian, World Bank

In the smaller urban centres, there's not the industrial pollution that there is in the megacities, so the issue then becomes one of pathogen destruction, rather than dealing with inorganics. And that falls in line with decentralised treatment systems; smaller, easier to manage systems, things like waste stabilisation ponds and co-composting of the organic fraction of solid waste with agricultural residues.
Graham Alabaster, programme manager, United Nations Human Settlements Programme (UN-Habitat)

In Burkina Faso, a man draws water for his vegetables from a wastewater stream (IWMI)
In Burkina Faso, a man draws water for his vegetables from a wastewater stream

Wastewater treatment is the best way, plus post-treatment health protection control measures. But maybe you just have to introduce a little bit of treatment, primary treatment, such as settlement in a deep, anaerobic pond. That's good because the helminth (parasitic worm) eggs will settle out, not 100 per cent of them, but enough to keep the disease more or less under control.
Prof Duncan Mara, School of Civil Engineering, Leeds University

Having simple water storage pools at the field site can reduce concentration and risk. Bacterial and viral content can be reduced ten times just by settling out particles. Moringa seeds, certain types of clay, and many more, can work as low cost binding agents, which cause settling of micro-organisms, and can be developed further.
Prof Thor Axel Stenström, chief microbiologist, Swedish Institute for Infectious Disease Control

Taking the message to town

My main message would be for municipalities to include urban and peri-urban agriculture in their planning stages. Not just housing or industry zoning, but urban green zones with agriculture in mind. Municipalities and governments spend astronomical funds in infrastructure but often lack watershed and landscape management. FAO assists local governments in the development of appropriate strategies, economic incentives and policies, as well as the provision of irrigation networks from wastewater treatment plants, to ensure availability of quality water for agriculture.
Sasha Koo-Oshima, FAO, Rome

We have a specific government institution to work with the municipalities on the issue of wastewater, and I'm happy to say that most leaders are embracing it and are leading by example. In south western Uganda we started with 40 towns, we said 'we are going to give you a clean water supply, but one of the conditions, every household must have an ecological sanitation facility.' Then we sensitised them about the value of sanitation, trained on how to construct the toilets. We are promoting them in schools and the urban centres.
Hon. Namuyanga Byakatonda, Minister of State for Water, Uganda

Municipalities should help farmers in the peri-urban areas to use wastewater as a resource in their agriculture, because it has many benefits. But then they should also put in place the type of by-laws and regulations that support the risk assessment and management process that WHO is now proposing in its guidelines. Municipal officers have to read the books, and WHO is ready to assist them with any challenges or problems they may face in the process.
Robert Bos, WHO

I think we need to focus not on the megacities but on the smaller urban centres, which have the urban characteristics, produce the wastewater, but have that linkage to the rural, agricultural hinterland. In these smaller towns and peri-urban areas there is a much better opportunity to look at things like wastewater reuse.
Graham Alabaster, UN-Habitat

Seeing the bigger picture

The World Health Organisation is no longer only allowing irrigation when a certain water quality level is reached, because most cities don't have the facilities to treat water to this level. The new guidelines suggest using multiple entry points. Start at the farm level, go the market level and the kitchen level and at each of those try to reduce the health risks as much as you can. That is a thousand times better than waiting for treatment plants.
Pay Drechsel, theme leader in agriculture, water and cities, IWMI

Wastewater poses serious health and environmental risks. (IWMI)
Wastewater poses serious health and environmental risks.

The step between farmers and consumers is even more important, that is the handling and storage activities that go on in the field. In Nigeria we found the number of parasitic eggs on pineapples was very high. This was because of after-harvest practices, when the cut pineapples were put on the ground. Therefore education on handling of crops will reduce risks to consumers considerably, and this applies to all high growing crops.
Prof Thor Axel Stenström, Swedish Institute for Infectious Disease Control

Wastewater irrigation of crops is only one pathway for disease transmission, and people are exposed to the same diseases through many other pathways, and some of them may be much more direct. We all talk about water, sanitation and hygiene, but from a disease control perspective, we should really be saying hygiene, sanitation and water, in that order. Personal hygiene, people having a safe, hygienic place to use as a toilet, and water to wash their hands with, are much more important.
Prof Duncan Mara, School of Civil Engineering, Leeds University

When we talk about wastewater, we also have to think about access to water in general for the urban poor. They don't have access to water and that is related to land rights, and farmers' legal rights of land tenure. In FAO we work with land rights divisions, as well as land and water divisions. In addition, we don't only target renewable natural resources in rural environments but also introduce the relationship between urban and rural. We have to overcome the mindset which counterpoises rural and urban development, as poverty knows no boundaries.
Sasha Koo-Oshima, FAO

Date published: September 2008


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