I think you may have two issues here. Obviously there's a leak. You'll have to figure out where that is, but I'd suggest it's either the radiator, a hose, or a freeze plug in the side of the engine. The water pump would be on the right side (passenger side here in the States) of the car, so your description of it would suggest it's not that. You'll have to diagnose this by sight or take it to a mechanic to see what they say.
The second thing which may be going on is there may be a problem with your primary fan or the power which goes to it. This may be a relay problem or the fan itself could be dead. The reason I'm saying this is because "usually" there are two different circuits and possibly two different fans which help cool the engine and the A/C. When you are turning the A/C on, the second fan would be kicking in allowing the cooling system to work as it should, as well as pulling air through the A/C condenser. If this is true, you probably wouldn't be seeing it overheat while driving it down the road with or without the A/C on. The relay should be in the underhood fuse box. You can change out the primary fan relay with a known good one and see if that does anything for you. You can also jump the connectors for the fan leads directly after pulling the relay out. If the fan(s) kicks on in either scenario, the relay is probably bad and would need replaced.