A staggering volume of water, sufficient to meet the daily drinking needs of nearly 40 lakh people, is going down the drain every single day in Lucknow. This colossal waste is not from leaky municipal pipes but from a common household appliance: the reverse osmosis (RO) water purifier.
The Staggering Scale of RO Water Waste
According to estimates by experts, the 'reject water' generated daily from domestic RO systems in the city is enough to provide drinking water for 33 to 40 lakh individuals. RS Sinha, convenor of the Ground Water Action Group, provided a detailed breakdown based on his study. The city uses approximately 1,700 million litres per day (MLD) for all domestic and other purposes. However, the actual requirement for drinking water is less than 1% of this total, amounting to only about 12 MLD.
A 2021 study by The Energy and Resources Institute (TERI) and Delhi University found that nearly half of Lucknow's 5.5 lakh households use RO purifiers. These machines produce about 6 MLD of drinking water. The crux of the problem lies in the technology's inefficiency: for every one litre of purified water, nearly three litres are wasted as reject water. This results in a daily wastage of around 12 MLD.
"Since one person drinks about 2.9 to 3.5 litres of water, this wasted water alone could meet the daily drinking water needs of 33–40 lakh people," Sinha emphasized, putting the numbers into a stark, human perspective.
Why Do Residents Rely on RO Systems?
The widespread adoption of RO systems stems from deep-seated concerns about water quality among Lucknow's residents. Common reasons cited include:
- Belief that tap water is unsafe due to bad odour, murky appearance, or unusual taste.
- Lack of trust in the municipal supply providing clean drinking water.
- Experiences of falling ill after consuming unfiltered water.
However, scientific data suggests this reliance may be largely unnecessary for most of the city.
Expert Advice: Maintenance Over Purification
SK Swaroop, Scientist-D and Officer In-Charge of the Regional Project Management Unit (RPMU) of the Central Ground Water Board (CGWB), challenged the need for rampant RO use. He stated that RO systems are technically required only when water has a very high electrical conductivity (EC) of around 2,250–2,500.
"In many parts of the city, groundwater EC ranges between 500 and 700, while surface water has even lower EC levels of 200–300. Therefore, there is no need to use RO systems," Swaroop explained. He attributed water quality issues to infrastructure problems rather than the source itself.
He pointed out that households store water in overhead tanks because supply is limited to roughly two hours each in the morning and evening. Damaged or poorly maintained supply pipelines and infrequently cleaned overhead tanks are the primary culprits behind contamination. Swaroop added that no salinity was found in the city's first aquifer and that most supplied water is safe for direct consumption.
"Regular cleaning of overhead tanks and proper maintenance of pipelines are more important than installing RO systems," he asserted.
The Path Forward: Conservation and Reuse
Experts propose a two-pronged solution to address both water safety and the crisis of wastage. First, municipal authorities and residents must prioritize the regular cleaning and maintenance of pipelines and overhead tanks to ensure a safe supply at the source, reducing the perceived need for RO systems.
Second, for households that continue to use RO purifiers, it is crucial to reuse the reject water. This wastewater, which is not suitable for drinking, can be perfectly utilized for activities like mopping floors, bathing, washing clothes, and flushing toilets. Implementing this simple practice could save millions of litres of precious water every day, easing the pressure on Lucknow's water resources.
The findings highlight a critical disconnect between public perception and hydrological reality, urging a shift from wasteful purification to smarter water management and conservation.
