A number of countries channel treated urban wastewater from towns and cities onto nearby farms growing vegetables and fruits. Israel has the most ambitious brown-water program of any country. The alfalfa in turn is sold as feed to small-scale farmers who raise guinea pigs and rabbits. One-third of the vegetables grown in Asmara, Eritrea, are irrigated with treated urban wastewater. In Lusaka, Zambia, one of the city's biggest squatter settlements irrigates its vegetable crops with sewage water from nearby settling ponds.
Some places apply the same concept differently.
For example, Calcutta, India, channels much of its raw sewage into a system of natural lagoons, where fish are raised. The fish are safe to eat because the lagoons soak up and clean the sewage. Unless urban wastewater receives some pretreatment, either from natural wetlands or sewage treatment plants, however, it can transfer disease organisms to vegetables and fruits and endanger human health. Such natural water treatment technologies as using wetlands often can be an alternative to modern water treatment systems that are too costly for poor urban areas of developing countries. Recycling waste for agricultural purposes by using oxidation ponds and aerated lagoons does not require as much land as is often assumed.