Although a defective water pump will leak coolant, this is not always obvious because it is dispersed around the engine bay by the drive pulley or fan.
If there is a persistent water loss, but checks on hoses show no apparent leaks, it is possible that the seal on the pump spindle is damaged and is allowing water to leak through the pump bearings. As a rough guide to pump condition and try to rock the pump spindle by moving the pulley up and down. If there is more than a fraction of the pump is probably leaking. Leaking pumps sometimes make a squeaking sound, but a squeaking pump is not necessarily leaking; carry out the spindle test before deciding to renew it.
Below are the procedures;
Drain the coolant and remove the top and bottom radiator hoses at the pump.
Slacken the generator mounting bolts and remove the drive belt. Where the pump has the radiator cooling fan attached, undo the fan-blade attachment bolts from the pump pulley and remove the fan. If there is insufficient clearance to remove the fan blades, undo the radiator cowl, or if necessary, remove the radiator.
Using a suitable socket extension bar and wrench, undo the attachment bolts or nuts around the outer edge of the pump. If the pump is linked to the cylinder head by a small bore by-pass hose, remove this. Draw the pump from the engine, if necessary lightly tapping it sideways with a mallet to jar it free.
Scrape any dirt and the remains of the old gasket from the front of the engine. Fit a new gasket to the new pump, holding it in place with non-setting sealant. Smear sealing compound on the gasket seating on the engine. If the pump has a by-pass hose fit a new one, with the new clips, first attaching it loosely to the pump stub.
Offer up the pump to the engine, if necessary fitting the by-pass hose on the cylinder head stud, thread the hose clip on the hose first. If appropriate, tighten the by-pass hose clips, then refit the radiator hoses, fan, and radiator, re-tension the fan belt and top up with coolant.