As Duncan says, what type of car is it?

Did you have air con on when you heard the electric fan?

Could be (brace yersel!) a knackared CHG or a cracked cylinder head or block.

Check your oil for level and any white gunge under the oil filler cap. 

You say you are loosing water but have no external visible leaks, well that could mean thatshe is leaking water into the engine thru a cylinder head gasket, cracked block or head.  If you have water in the engine your oil will look like mayonaise.  Also look for plumes of white exhaust gasses as you may have a water leak into the combustion chamber which will not emulsify your oil but will consume water and chuff out loads of steam.  Low water level will mean your engine temp will rise.

Give us a few more bits of info on the car, engine, model, age etc and we will be able to help a bit more.

Get a compression test done as soon as.

Andrew

Alan

Whats the exhaust gas look like?  Is it white and looking like steam when the throttle is floored?

The water has to be going somewhere and if its not going into the oil it must be going somewhere else.

Get a pressure test done on your cooling system.

Another thought, check your rad/expansion tank cap for signs of overflow.  Someone on one of the forums here had a dodgy rad cap which allowed the hot expanded coolant to leak out of the system when the temp got up a bit.

What is your heater performance like?  You may have a leak in your heater matrix which will not leave a puddle on the ground under the car but will make the carpets and any insulation behind the dash a tad soggy.

Andrew

Hmm

Me puzzeled too.  Could be a very fine spray leak that only happens when the engine is running.

Get her fully warmed up, park, get out and look at the ground somewhere nearby to make sure there are no oil puddles or water puddles.  Move the car over that piece of ground and leave her there with the engine ticking over while you open the bonnet and have a good look around for any water spray.  Check the ground beneath, if there is water on the ground you can then trace it directly upwards to whatever part of the cooling system that resembles a sieve.

Andrew

I had this too it turned out to be a cracked rubber pipe, tucked away where i couldnt see it. It was only leaking when it was up to full temp, a fine jet was spraying out all the water. Your car is fairly old, so expect the rubber hoses to be perishing at this age....which mine did too..... 

nero wrote: I'm not a mechanic, but would performance drop off if water was leaking into the engine?

Ever heard of water injection?

Get a coolant pressure test done as this will show any external leaks and will also tell if there is no leaks but the pressure drops, it will be internal. What car is it?