Dirty water in engine coolant reservoir - 1995 Mitsubishi Space Wagon (2.0 Automatic)?

Hi, we're looking to buy a Mitsubishi Space Wagon for the family, 2.0 petrol automatic. Had a drive today, seems ok, no smoke out the exhaust, bodywork good for age of car, little oil on the engine but nothing major. Two worrying things, the fan belt squeaks on start up but the owner suggests that its being tightened today; the other thing is the water in the engine coolant reservoir is a muddy brown colour. Is this ok or should I be asking more questions and be wary? Any other advice on the Space Wagon, good or bad will be greatly appreciated. Cheers in advance, ask away if I;ve missed anything