My water pressure is 30psi, water flow is 14-15l/min, so i reckon i will need one.If you look at the booster pump Purefreedom sells the you will see that they regulate the flow and pressure output with valves.
Large Booster Pump with Fittings - Pure Freedom
Large booster pump pack. Suitable for boosting the pressure into 40 inch reverse osmosis systems. Contains rotary vane brass bodied pump head, coupling to attach to the IP55 rated motor, this motor is 230 volt 50Hz 0.37 kW 3.2 amp 1370 rpm. The motor will require connection to mains electricity...purefreedom.co.uk
Speak to @doug atkinson at Daqua. He sells a booster pump. You need to ask how he controls it's on/off operation.
What is your tap water pressure and how many litres does your outside tap deliver per minute fully open?
If you have reasonable water pressure, then you could well not need a booster pump @kolk1n . Booster pumps make a lot of noise, which can create drama with neighbours.
Daqua doesnt have 4040 booster pump in stock thats why i am checking elsewhere.
I know the one from grippa is on the expensive side but it comes with the manual.
My lst purchase from purefreedom lacked instructions, proof of purchase etc so i am not sure i will manage without that.