Water Flow.Water flow measures how much water is delivered over a set period of time. For example if a 10 litre bucket under a tap takes 10 seconds to fill then the flow rate is 1 litre per second. Water Pressure.An example of pressure concerns a cold water storage cistern that is used to supply water to a basin in a bathroom upstairs and a basin in a downstairs cloakroom. You will notice that the pressure at the downstairs tap is considerably more than that at the one upstairs. The increased pressure is due to the height of the cistern in relation to the tap. Take a hose with an adjustable nozzle. With the nozzle open slightly, there will be a high pressure jet of water but the amount of water coming out. Open the nozzle fully and the pressure will be far less but the amount of water coming out (the flow rate) will be far greater. There are devices available to measure water pressure and water flow. You may see a professional plumber from Clerkenwell Plumbers using these. Where a new plumbing installation is being designed, measurements of both the incoming mains water pressure and flow may be needed to help with the design and specification process.Mains Water Pressure Gauge.Using a mains water pressure gauge, the pressure at an outlet can be measured. This device has a threaded connection to fit the outlet and will measure the water pressure in bar.Water Flow Weir Cup.A boiler installer like a Clerkenwell Plumber may need to check there is a sufficient flow rate for installing a combi boiler. There is something called a weir cup that professionals use for accurate flow readings. It reads both litres per second and gallons per minute. If a flow rate needs to be reduced, a weir cup may be used to measure and then accurately adjust the flow rate to meet the operating flow rate required to suit an appliance manufacturers specification.