Dear Girishji,
Your question relates to Greywater, the water resulting from washing or bathing.

It is estimated that 42 to 79 per cent of household greywater comes from bathrooms, 5 to 23 per cent from laundry facilities, 10 to 17 per cent from the kitchen sink and 5 to 6 per cent from the bathroom sink. Various studies have indicated that the amount of greywater generated per person per day varies from 96 to 172 litres. That's a huge amount of water being wasted in the world every year. If all this water could be put to use, then a lot of water could be saved.

Now, greywater contains recyclable organic materials such as nitrogen, phosphorous and potassium. These materials are pollutants when discarded into the environment. When responsibly recycled, however, they can be beneficial nutrients.

Organic material is a resource, rather than a waste. All wastewater contains organic materials, such as food remnants and soap. Microorganisms, as well as plants and macroorganisms, consume these organic materials and convert them into beneficial nutrients. In a sustainable system, wastewater is made available to natural organisms for their benefit. Recycling organic materials through living organisms naturally purifies water.

But greywater can't be used directly to water plants because of it's chemical content. It can't be used to recharge a borewell as it will contaminate groundwater. But it can be used for many other agricultural purposes. Methods have been devised to use greywater for landscape irrigation, certain types of kitchen gardens, soilbeds, soilboxes and ponds. But as greywater may contain large numbers of bacteria that could be disease-causing organisms, care needs to be taken to utilise and channel it properly.

For more information on how to do that, log on to www.greywater.net or http://doityourself.com/garden/greywater.htm. The Humanure Handbook by Joseph Jenkins also explains the whole issue of wastewater and how to utilise it.

Dear Kashyapji,
You heard right. Wood smoke is as bad as cigarette smoke. Tobacco smoke and wood smoke are similar in many ways. Suspected carcinogens in cigarette smoke, such as benzo(a)pyrene and formaldehyde, are also present in wood smoke. Assuming that an average smoker smokes around 40 cigarettes per day, the exposure of a person cooking with biofuels can be compared to both active and passive (second-hand smoke) smokers.

Active smokers inhale pollutants with every "puff", but a filter absorbs some of the toxins present. In contrast, both passive smokers and people who cook with biofuels are exposed with every breath.