Hi my Impreza has just started over heating anyone got any ideas?    The water looks like it's changed colour . Thanks 

What colour has it gone, brownish?  Are you loosing coolant? Is it overheating when moving or just stand still? Have you checked the oil dipstick?  Any smoke from exhaust when warmed up?

Sorry for all the questions but will help with diagnostic. 

How badly ? Any visable signs of leaking water ? Pinhole cracks on the radiator are common on stock units. Could be something as simple as that or a broken thermostat, worst case it's head gasket related

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Your oil is contaminated  with coolant. Worst case is blown head gasket or cracked/warped head

Yes looks brown ish not losing water. Temp is OK while moving fan kicks in temp keeps rising while standing iv not let it boil took it home parked it 

Could be really dirty coolant. When did it last get changed.?

It's booked in for a service Wednesday, I checked oil and water the other day it wasn't brown then 

Check the inside of the oil filler cap. It nay look like cottage cheese. If there is a the white residue that's a sure way that water is in the oil system.

If it's happens that fast then it doesn't look good. How far did the temp gauge go?

No white crap on oil cap, temp went up to just before red, iv got everything crossed its not head but knowing my luck it is 

That's quite close to blown gasket temps. You might be lucky though. Some survive some dont

Now that I think of it. It could be a blocked hose or rad. 

Use gas analyser to sniff for exhaust gasses at the rad cap port. if passes that, inspect coolant pressure holding/psi-value, inspect thermostat for function, finally fully drain flush & refill coolant & see how temp runs in normal use  ...

Just wanted to thank people for there replies. Turns out there was a small water leak and car is running to normal temp now 😀

Excellent news