Due to the location, the best bet has to be the water pump.
Having said that, you have the radiator hoses at that end and the rad' has a bleed screw on the back, also at that end. You need to check where the water is coming out from.
Water pump is a cam-belt off job... fit a new belt and tensioner bearing (£25-odd from S4P but make sure you get the right pitch cam-belt. Their kit is for 8mm pitch.. engine numbers 900,000 odd onwards). Older engines use 9.25mm pitch.
Ralf S.