ABSTRACT
Use of wastewater from households, i.e. grey water for irrigation, has become a common practice, especially in Indian villages. Over the last two decades, due to a decline in annual rainfall, such practice has been purposely adopted by farmers in arid and semi-arid regions. Such practice in India is called “blackwater farming”, as it is in countries like Australia, France, Germany, the UK and the USA. Various studies have revealed that an individual uses water on a daily basis between 15–55 and 90–120 L/day per capita and reuse of this water not only reduces pressure on fresh water requirements but also saves the water from entering unnecessarily into septic tanks. There is an economic benefit in using wastewater as it saves water and sewage disposal. Such use can be a breakthrough if we are concerned about sustainable use of water, but ill effects due to use of untreated wastewater cannot be ruled out. The health hazards due to inherent toxic chemicals, heavy metals and microorganisms which can contaminate the soil and edible crops are poorly understood. The World Health Organization (WHO) published general guidelines in order to protect public health and reuse wastewater in agriculture and aquaculture in the year 1973; these guidelines were updated in 1989 and 2006, keeping in view risk factors. Some countries, especially developed countries, have adopted the WHO guidelines and follow some standards in order to use grey water; however other countries do not have any strict guidelines on the use of wastewater as there is no cost-effective basis to justify the extra expenses involved in its treatment. WHO recommends taking health protection measures to reduce risk; for example, direct human contact with untreated grey water should be avoided; irrigating lawns and public gardens should be avoided unless they are only for ornamental purposes and there is no possibility of direct contact with children or pets/animals. Subsurface irrigation can be used as it reduces the risk of contact. If crops are to be used for consumption, irrigation should be strictly to those crops that are cooked before being eaten. However those crops that are in direct contact with the soil, like potatoes (Solanum tuberosum) and onions (Allium cepa) or eaten raw as salad, for example, lettuce (Lactuca sativa), carrot (Daucas carota) and tomato (Lycopersicon esculentum) should also be avoided.
