We complain about the muck that our cities are mired in, often forgetting that it is us who generate it – untreated sewage from households is the biggest source of water pollution in India. In many cases, neither households nor municipalities have adequate systems to treat and release/reuse it appropriately.
Of the freshwater we use in a household, about 80% becomes wastewater. This wastewater is broadly of two types – greywater and blackwater. Greywater is simply soap water, i.e., water from bathrooms, washing machines etc. The key contaminants in greywater are phosphates, and foaming agents from soaps and detergents. Blackwater is wastewater from toilets and kitchens, that has organic content. It contains nitrates, pathogens, carbonaceous matter from our urine and fecal matter, and also chemicals used in toilet cleaning. Since greywater contains fewer pathogens than blackwater, it is easier to treat and reuse.
On average, a four-member household generates 360 litres of greywater (90 litres per capita), and 120 litres of blackwater (30 litres per capita), daily. Usually, greywater and blackwater are not separated, and both enter the sewerage system. Overall, urban India generates about 62 billion litres of sewage daily, but has the capacity to treat only 37% of this; and even this capacity is not fully utilised.
Industrial wastewater is also a major pollutant in Indian cities. Though the overall quantity of industrial wastewater is low compared to sewage, it contains far more toxic substances like heavy metals, pesticides, radioactive sludge etc. Many formal and informal industries do not have adequate facilities to treat their effluents.
Both domestic and industrial wastewater are dumped into surface water bodies like lakes and rivers continuously. These water bodies become toxic, heavily silted and their oxygen levels get depleted due to a process called eutrophication. They die in a few decades, becoming unfit for human use and for sustaining aquatic life.
About two-thirds of surface water in India is estimated to be polluted, mainly by microbial contamination due to sewage. Wastewater also percolates into the ground, contaminating the groundwater that we consume. Crops irrigated with wastewater, fish from polluted lakes, milk from cows grazing on such lake banks, all contain toxins. Our toxins find their way back to us, either directly through the water we use, or through the food chain.
Wastewater is a significant public health hazard. Diarrhoea, mainly due to microbial contamination of water, is a leading cause of death in India. Industrial waste like heavy metals have long-term health effects. They can accumulate in human body upon continued exposure, and can cause severe illnesses like cancer and neurological disorders. Chemicals used in toilets also become part of wastewater; hence we should reduce their usage and also be mindful of the type of products we use.
However, wastewater is simultaneously a resource, if used wisely. Domestic wastewater treated to appropriate levels, has multiple uses. It is ideal for irrigation since it contains the nutrients nitrogen, phosphorous and potassium, which are the key components of fertilisers. Greywater generated at home can be treated and reused too. These are ways to ‘close the loop’, i.e., put water and nutrients in a loop rather than release them as pollutants. Such solutions are integral for sanitation as they have the twin benefit of resource reuse and diminishing a public health risk.
Cities continue to choke on their own polluted surface and groundwater, while taking water from distant sources. In Bengaluru, only about 40% of sewage gets treated, and less than 1% gets reused. Every state has a Pollution Control Board (PCB) to monitor and control water pollution. PCBs mandate bulk generators of wastewater – including industries and large apartments – to treat it. Bengaluru is the city with the highest number of apartment STPs in the country. However, smaller apartments and households here continue to discharge sewage into storm water drains.
Instead of releasing wastewater, you can collect the greywater generated at your home, treat it, and reuse it for non-potable purposes like toilet-flushing, car wash and gardening. Water treated to higher standards, using more expensive technologies, can even be used for drinking.