My check engine comes on when its cold or damp outside and now since its winter i have noticed coolant leak around water pump. does my water pupm need changing and could that be why my engine light was coming on? how costly is it to have fixed?

There are litterally hundreds of reasons why your Check Engine Light could becoming on. The only way to find out is by having your engine computer scanned for fault codes. If your water pump is leaking it needs to be replaced regardless of whether or not it is the reason for the check engine light coming on. I don't know the labor rates where you are...come to think of it, I have no clue where you are...But what I can tell you is that the water pump on your car is not very expensive at all compared to most of the water pumps I change. It's one of te easiest water pumps out there...not much labor involved.

Please check for the engine oil level and the quality of the oil within as if the temperature goes cold there will be lesser pressure on the oil as the viscosity drops.
If so change the oil and filter, check the fuel filter .
Now it is important that the car maintenance must be done according to the schedule of the maker.
So please check on your log book to confirm and do the necessary schedule which includes the topping and changing of fluids and coolants.