for the average RO i use a normal hose connected to the outside tap, my outside tap was leaking, and they may well leak allot if you have those rubbish plastic hoselock connectors anyway i put a new tap on with just a normal 1/2 '' outlet like a copper pipe, then used a jubilee clip to tighten it on, there are no leaks atall! much better
as for the 'beast' ian is mentioning well for that still i use the garden tap for because its supply comes from a 300gallon tank, the tank supplies the normal tap water to the ro unit via the pump which is constantly on to supply enough pressure to the twin 4040s, the tank is there to ensure theres enough water for the pump to suck if the pump was connected straight to the outside tap, then the pump would be running slightly dry as the tap pressure cannot supply enough water to it. This would usually be supplied via mains water pressure.
Usually you would only need a booster pump to run through the ro if your pressure is low. You dont really need another plumbing source just for the Ro like a washing machine or dishwasher has, its just unnecessary.