Overheat and low coolant

I am not at all handy with vehicles and this is the first problem I have had with my 1991 Cruising Cabin.....overheated on motorway last week, temp gauge shot up almost to Red. Pulled over immediately.....hardly any fluid in the coolant tank....filled it up with water...it took a lot to fill it and managed to drive 75 miles home with a steady gauge, but looks like it has lost a lot of fluid again and the engine was really hot - is there anything I can easily check before sending it to the garage - was told it sounds like one of three things:

leaking hoses
leaking rad
cracked water pump

I am in the North West of England...any help/advice welcome

Check (or just replace) the viscous fan coupling boss.
That's the primary point of weakness - if that stops working you're going to overheat because of the radiators location tucked inside the van.

GPW wrote:

Check (or just replace) the viscous fan coupling boss.
That's the primary point of weakness - if that stops working you're going to overheat because of the radiators location tucked inside the van.

Thanks GPW, I am taking it to the garage tomorrow so will ask him to look at it.
There is a lot of orange sludge in the coolant reservoir and signs that it has got onto the engine and main hose from the radiator
I am hoping it just needs a flush and replace of coolant and perhaps a leaking hose or two