If your car has developed a water leak then you may not have to rush out to buy a new radiator just yet. I recently found that every few weeks my car was showing the coolant low warning light and sure enough, when I checked it was quite low. This seemed to get more and more often when it got to the point I would sometimes need to top t up daily just to make a few small journeys.
I invested in some RadWeld to put in to the coolant system, which should effectively block up the leak. The solution is put in to the engine and ran round for about 30 mins after this time the engine is switched off and if the Radweld finds a leak and starts to escape it will solidify blocking up the leak.
Unfortunately this did not work for me, so I had convinced myself that I needed to buy a new radiator, but when I filled it up I started to notice that the water was actually coming from the bottle where it was being filled and it was the container that was leaking not the system, meaning it would be a quick fix at £20.