Hello
Vancov
On the presumption you currently have a an external water barrel and a plug in submersible pump, then the pump manufacture may offer a direct connection hose, which goes from the sites tap to the water inlet where you would normally fit the pump. However its not as simple just using a hose and a pump connector.
Mains water pressure at a site tap can easily exceed 6Bar which is far too high for the pipework and water appliances fitted inside a caravan. To overcome this, the supplied connection hose has a pressure limiting valve fitted to it which limits the pressure to the caravan to less than 1.5Bar which is the maximum safe working pressure for the caravan. The pressure limiting valve is essential. Do not confuse it with a flow restricting valve which does not limit pressure.
Generally these systems do work, but very occasionally if they can go wrong then it will damage the caravan.
They will of course only work if there is enough water pressure and flow at the sites tap. On a large site the water pressure at any tap may go up and down a lot becasue other pitches are also using water. This might inconvenience you when trying to shower or some other activity.
Some caravanners also report they lower flow rates using the direct hose compared to using their pump.
I personally suggest you use the ball valve system suggested by Parksy and others, it really is much safer, and prevents damage to your caravan if it does go wrong.