Posted on 12th October, 2011


Traditional screw head water taps are found in most dwellings but they waste energy when hot water is run for longer than necessary; i.e. the tap is not always turned off as soon as it could be, so unused hot water runs out of the plug hole. If we replace our screw tap with a push on / self closing tap how much could we save in terms of energy costs?

The average screw head tap will deliver approx 12 ltrs per minute when turned partially on. On average a screw head tap is left on for 15 seconds. Assuming each person on average washes their hands 4 times per day, this equates to 12 ltrs per day per person. On average the self-closing taps will reduce this to 6 ltrs per day because the flow rate of a selectable flow rate push tap can be adjusted to run from 4 ltrs per minute and the time on can be reduced to between 3 and 11 seconds.  The push tap cannot be left running, as it self closes.

Over the period of one year, for a family of 4, the total hot water used at one tap to wash hands is 17,520 litres for a normal screw tap and 8,760 litres for a push tap.

Irregardless of the temperature at the tap* (recommended maximum of 410C), water should be stored at temperatures under 200C or above 600C. I reckon that the average temperature of water in my cold water tank is about 100C.

Here are the sums:

Screw Tap: Heating 17520 litres of water from 100C to 600C (using electricity at 17.8p/unit) will cost:

17520 kg x 4186 J/kg0C x 500C / 3.6MJ x £0.178 = £181.31

Push Tap: Heating 8760 litres of water from 100C to 600C (using electricity at 17.8p/unit) will cost:

8760 kg x 4186 J/kg0C x 500C / 3.6MJ x £0.178 = £90.65

Payback: A push tap at £32.00 fitted using DIY (so zero fitting cost) gives a payback time of £32.00 / (£90.65 / 365) = 129 days or about 18½ weeks


Any questions or thoughts? Please post a comment.


* A mixer tap or hot and cold taps provide water at the correct temperature in the sink, bath, shower, etc.

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