1996 Vauxhall Astra car over heating

Engine Cooling problem
1996 Vauxhall Astra Front Wheel Drive Manual 13100 miles

hi, I bought my vauxhal astra ls 1.4 last week and knew that there was an advisory on the mot for a small weld to the exhaust and was told that was the only problem the car is very clean inside and out and has a full yrs mot on it I drove it home and it got a little warmer than it should have so I topped up with some water. But now the car is going up to 100 after a few miles 3-4 when I stop the fan is kicking in is it the water pump? What could be wrong with the car?