Basics to know about, household water pressure!

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Pressure is a measure of how much a liquid is compressed. It is not the ‘force’ exerted by the water at an outlet. The force is a measure of how hard the water can ‘push’ at an outlet. The pressure of a contained water system will be the same no matter what the size of the outlet. The force – however – is dependent on the outlet size. The smaller the outlet, the greater the force.

Reduce the size of an outlet on a hosepipe by covering it with a thumb and the water emerges with much more force as evidenced by the distance that it sprays.

There are many units in which pressure is measured. These include Atmospheres, Bars, Inches/millimetres of Mercury (mmHg), PASCAL’s and kiloPascals (kPa), Pounds per square inch (PSI). We are familiar with Bars when inflating our motorcar tyres – typically 2 Bars. This is the same as 200kPa. The pressure to which the Earth’s atmosphere is squeezed varies as the weather systems change, but is generally about 1 Bar. On household barometers, this pressure is often given in millimetres of mercury where 1 Bar is the same as 750mmHg.