if it's needing a pint or so of water, there's a small leak somewhere, if it's the head gasket you'll see whitish/greyish gunk around where you put the oil in. when the temp gets to high the fan comes on to help cool it. around town maybe your not driving it long enough for temp to go up. normally when your on a long run(motoway) the temp should be ok as your constant blow of cool air through the rad. get someone to have a look for you