Whats the best fluid model to use for water?

[HappMatt]

I realize this seems basic, but I'm looking around on the net and i just cant find the answer. I'm running a ANSYS simulation of heat transfer through a pipe and I was using a Newtonian model, but then someone mentioned about using the power model. I cant seem to find the definitive answer as to which is best. The flow is in the transition Reynolds flow regime between 56F and 112F on the tube wall.
thanks

 

[CFDFEAGURU]

If you are still working on this, are you using ANSYS traditional or Work Bench? What is the pipe material?

Thanks
Matt