1997 cadillac deville is loosing water but cant find a leak and keeps over heating

Immeadiately check the oil dipstick. If the oil is grey, the gaskets (Usually in the head) between the cooling system & the oil is blown, & water is getting into the oil. This usually means that the head has gotten so overheated in the past that it is warped & not sealing the gasket properly. This is very serious, & the gasket will eventually blow, & the engine will not run much at all. The overheating will get bad enough, that with the above, u will blow the engine.
That is the bad news.
It is also entirely possible that u could be losing cooling fluid (You should use that, not just water) through ur heater radiator inside the car, & that stuff is not good to breathe. You'd notice the smell.
What u can try - If ur oil is still black or tan, not grey, is radiator additive, which will usually seal small leaks. Get it at the car parts section of any hardware store.

Well u need to use a antifreeze tester to test the mixture first off , then run the cold engine with gloves on squeeze the top rad hose tightly & see if within a few Min is if pressure builds up forcing ur hand open, plus watch & listen for the fan to engage within 5 Min is or so too. If the upper hose does not give back pressure then the thermostat is no good , if the pressure is there & the fan is not engaging check the fans connections ,it is ground ,relays & sensor , then get the fan tested.
One main problem is if you've too much water in the coolant system the engine will burn of water bec its getting too hot & u will be thinking theres a leak when there is not any more then likely if you've not seen anything leaking.

Hope that helps & best of luck.By the way once u check the mixture , be sure to allow the new antifreeze to mix into the engine a bit before retesting mixture.Plus be sure to check under the car , all hoses , rad & heater core hoses & clamps for any possible leaks & try parking on dry surfaces so u can look under the car for any obvious leaks too.

headgasket,waterpump,coolant crossover are all common leaks

The Intake Gaskets , Head Gaskets , Water pump , Hoses ,Freeze Plugs ,Or Heater Core Could Be Leaking.The Best Thing To Do Is First ,Check To See If A lot Of Steam Is Coming Out Of Your Exhaust. If Yes Probably Head Gasket.Then Check Oil Fill Cap For Signs Of Moisture.If Yes Probably Intake Gasket.If Its The Heater Core You Should Smell a Sweet Smell When You Turn On Heater.The Other Things Can Be Checked By Pressure Checking System.