Have you ever smelled a blocked sewer? The stink goes right through to the marrow. As you shudder and roll up your car windows, do you think you are part of the problem? Well you are, says Sunita Narain, Director of the Delhi-based Centre for Science and Environment (CSE).

Narain has been working actively with the chairperson of the Environment Pollution (Prevention and Control) Authority, Bhure Lal. Speaking at a talk titled 'From Your Flush to the River: Delhi's Responsibility for a Clean Yamuna', Nairain stressed that Delhi gets more water than it needs. The problem lies in improper sewage disposal and the "ecologically mindless (and) inequitable" distribution of water. Parts of Delhi get only 30 litres of water a day per capita, whereas the posh NDMC (New Delhi Municipal Corporation) areas and Delhi Cantonment get about 400 litres.

More water, she says, only means more sewage. Cities like Copenhagen are actually cutting down on water allocation because of this. Narain says that Delhi gets 600 million gallons of water every day, and 80 per cent of this just goes down the drain. Only 20 per cent of it is used for cooking or drinking; the rest is used for cleaning, bathing and flushing.

Delhi's six main sewage drains - Najafgarh, Shahdara, Maharani Bagh, Sarita Vihar, Barapulla and the drain near Sen Nursing Home - contribute 90 per cent of the flow and 80 per cent of the pollutants in the Yamuna.

The Yamuna Action Plan notwithstanding, the river is dead soon after it enters Delhi. The river is healthy at Palla, where it enters Delhi. By the time it reaches Okhla, though, the Dissolved Oxygen (DO) levels actually dip to zero, except during the monsoons. DO levels are considered an indicator of the health of a river. Water with about six mg of DO per litre is potable; and water with four to five mg of DO per litre is of bathing quality.

Coliform levels - an indicator of faecal matter in rivers - are also high. At Palla, coliform levels are 6,500 per 100 ml. The acceptable standard is about 5,000 per 100 ml. And by the time the river reaches Okhla after meeting the Shahdara drains, coliform levels touch a chilling 450 lakh per 100 ml.

The flush toilet in our homes - and not the slums on the banks of the river - are to blame. In fact, these clusters are usually not even connected to the sewage system; and they don't use flush toilets. Narain's figures say that only 50 per cent of Delhi's population is connected to the sewage system.

Delhi has only 17 sewage treatment plants (STPs). Data on how these STPs are functioning is depressing. According to Central Pollution Control Board (CPCB) figures (January 2004), 73 per cent of STPs in Delhi are under-utlised and only 10 per cent are running to capacity.

Narain visited various STPs and saw first-hand how wastewater is purified and cleaned. On her visit to the Yamuna Vihar STP, she was even offered treated water to drink. The water had been purified to 15 BOD per litre (biochemical oxygen demand, an indicator of water pollution). The CPCB classifies water with two mg of BOD per litre as Class A, potable. Water with three mg of BOD per litre can be treated with sedimentation and filtration alone. Normal wastewater - water mixed with domestic sewage and industrial waste - has a BOD of 200. Impressed, Narain asked to see the outlet pipe. Shockingly, she was told that the treated water is thrown back into the drain. After all the effort and expense on treating the water, it is mixed with untreated effluent to dilute BOD levels. "To mix treated water with dirty water instead of finding use for it is unacceptable," she says.

Narain has, in fact, long stressed the ecological impact of one of modern civilisation's big blessings - the flush toilet. CSE has been advocating the use of the dual-tanked lavatory - a smaller tank for urine and a large one for solid waste - as being far more ecologically sound.

Narain also says, "We do not pay for our water cost". Delhi Jal Board's annual budget is about Rs 500 crore, of which it recovers only Rs 260 crore. The cost of water is Rs 4.70 (1US$=Rs46) per 1,000 litres, whereas we pay 53 paise per 1,000 litres. Of course, she says sardonically, we pay Rs 10 per litre for mineral water. The figures prove that the government has to heavily subsidise the ablutions of the rich and middle classes. We must pay more for the water we use, she said. Although this message found little favour with her audience, Sheila Dixit - Delhi chief minister and chairperson of the DJB - was listening. Just two days later, she announced a proposal to hike water charges.

"This is not an academic exercise, it's a call for action," says Narain. The acute water crisis, riparian conflict, our heavy dependence on and depletion of groundwater calls for quick action.

The action plan is simple. To clean up the Yamuna:

• We must pay for the real cost of water.

• We must flush less often and avoid use of harsh cleaners.

• Move the authorities to get all the sewage treatment plants working to maximum capacity.

• Finally, there must be a charge on sewage and water based on usage. Mumbai charges a 60 per cent sewage surcharge based on water usage. Narain, though, says that we should ideally pay an 80 per cent sewage surcharge.

In short, we must clean up our drains, our lavatories and our lives.

The ideal system would be one in which our water consumption is placed below the capacity of our water treatment plants, Narain says. "We should remember, we all live downstream."