I live in an area where the water pressure is pretty low, and when moving into my house noticed that there was a pump installed to assist the shower in pumping out water - when I turn my shower on, the pump turns on with it. Just purely out of interest - could somebody explain how a pump knows to turn on - in other words, what's its trigger?
"what's its trigger" it depends on the pump. It can start when it detects a change in pressure when you turn on a faucet or flush the toilet, a sensor will detect this drop in pressure. (look up the Bernoulli's principle) It can also start when it detects water flow. In this case, it is usually not a sensor but a vane that moves from the flowing water.