We did the "1/3 full with cold water" and by the time the pool was full, the water was still too cold for me!

:
You should've seen DH & MIL running up and down the basement stairs as they were boiling water and bringing it down to the pool to warm it up! (I got a new microwave out of the deal though since they burnt it up with constant use!)
I only ended up in the pool for 5 min. before DS was born, and was very dissapointed since my labor was VERY intense and I could've used the relaxation from the water!
I would recomend filling it with warm water for a little bit, then switching to HOT and COLD at the end to adjust as needed, but that's just me!
DEFINATELY do a trial run.....that would've saved us!