• Question: When you turn on a water tap, how much force comes out of the tap?

    Asked by anon-267545 on 11 Nov 2020.
    • Photo: Iain Tullis

      Iain Tullis answered on 11 Nov 2020:

      Water is under pressure, or force per area. In the past, water was pumped up a tower (a water tower) and then the pressure was the head – or height the tank was at. The modern way is to do away with the water tower and have a pump that controls the water main pressure. In the UK the water suppliers’ statutory service standard level of mains water pressure is 10 metres/head – about 1 atm, or 100 kPa. This means that (at least) if your tap is 10 m high, the water would just about dribble out from the tap – there might be more pressure, but it’s not guaranteed. A standard pipe diameter entering the house is 25 mm diameter. Then the force the main stopcock in the house needs to apply to close the tap is about 50 N (work out the area of the pipe and multiply it by the pressure keeping units consistent)

    • Photo: Sam Geen

      Sam Geen answered on 11 Nov 2020:

      I was looking at this and came up with a similar number to Iain’s but didn’t believe that the water pressure from a tap could lift a 5 kg weight, but apparently it can? I guess it makes sense that water pressure has to be enough to lift the water itself up your house.

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