[jdmccright]

Two problems with using plain ol' water:

1) Using just water dilutes the mixture of water/antifreeze in the cooling system. Ideally it is a 50/50 or 1:1 mix of water to antifreeze. Enough dilution and the coolant mix won't protect your system from freezing in the winter or prematurely boiling in the summer.

2) Plain ol' water was alot of dissolved stuff in it like salts, minerals, and even undissolved yet suspended sand & silt. Problem is, when water is heated up, all this stuff actually resolidifies as scale (just like your bathroom shower head and fixtures) INSIDE your engine and radiator. It is STRONGLY suggested to buy distilled water to make up your 50/50 mix.

By now, I'm guessing your system is kinda out of whack, but more importantly you should find out where all that stuff is going before you pour more water and expensive coolant into it. The most likely spots for leaks are at the conections between the radiator and the engine (those two big black hoses that go from the top & bottom of the radiator). Look for color-tinged (it can be green, yellow, or orange tinted, depending on the type of coolant used...there are more than one) whitish deposits or wet drips under your car for clues where its coming from. A lot of times, a turn of a screwdriver will tighten up the clamp that keeps the hose from leaking.

Check your owner's manual for the right kind of coolant to use in your car. Then go to the store. You can buy premixed coolant (usually labelled "50/50") for your car, but if you have been doing this a while and the loss is substantial, you might consider having it drained, flushed and refilled with the right stuff and have them fix the leak. Hope this helps!