You have to add water often? Hmm, is there smoke coming out of the tailpipe? Check the oil... is it a milky color?
you must have a leak, does it overheat only when water is needed?, joef is also right, check the water to see if oil is present, and check oil to see if it looks milky, you can have an intercooler broken or maybe your engine head. let us know... hope this helps
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