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How much water does an urban citizen need?

In India, the design of water supply systems has been done using certain standards. Currently the standard being used is BIS 1172: 1993, reaffirmed in 1998. This specifies a consideration of use of the following:

For communities with a population of between 20,000 to 100,000 — 100 to 150 litres per head per day

For communities with a population of over 100,000 — 150 to 200 litres per head per day.

In its previous avatar there was also an attempt made in IS 1172 to understand the break-up of this demand which was then put as 135 litres per person per day. The break-up was as follows:

Bathing: 55 litres

Toilet flushing: 30 litres

Washing of clothes: 20 litres

Washing the house: 10 litres

Washing utensils: 10 litres

Cooking: 5 litres

Drinking: 5 litres.

It is up to each one of us to say whether these numbers ring true. However, a detailed indulgence has to emerge for ‘true water demand’ to be understood and thus for systems to be designed with a desired outcome which can be of two kinds:

(a) ensuring that standards are met so that public and individual health and hygiene is maintained

(b) outcome could be to drive water efficiency when the actual demand exceeds this standard.

Understand the issue

In an era of water scarcity and limited supply other nations such as Germany are driving down consumption to 100 litres per capita per day. Granted we are in a tropical climate for the most part, an effort needs to be made to understand true demand and consumption.

Does bathing actually require 55 litres per day? Of course with a teenage son or daughter this may seem less but for a responsible water user this number seems appallingly high. Can washing of utensils be actually done with 10 litres? What about the garden and landscaping requirements which many apartments and homes have?

Our experience has shown that high income households tend to consume 250 litres (per head and above) and sometimes as high as 600 litres. Many homes on the other hand make to do with as little as 40 litres per person per day.

On the other hand the question can also be how this amount (of water) can be made accessible to those who have no piped connection?

While some water-efficient devices such as low flush toilets and low demand showers are available in the market, there is no conditionality being imposed that all water-delivering devices should meet certain efficiency norms. It is essential in a water-scarce country like India that all taps, showers, washing machines, flushes, and garden hoses be strictly water efficient.

While on the one hand water conservation and recycling can drive down per person water demand, it is also true that certain systems need a minimum consumption to keep the system going. Underground sewage systems, for example, need at least 150 litres for what is called self-cleansing velocity. Less water use can result in sewage pipes choking and getting blocked.

Water meters

Every individual home and apartment, if metered, can measure its water consumption and compare with standards. Price signals can be sent to ensure that those consuming over the standards pay a high price.

Understanding how consumers are responding to water availability will enable better design of systems and result in efficient use of water. Our cities need to respond urgently. That would be water wisdom.

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Printable version | Sep 18, 2021 9:37:57 PM |

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