Yep, no way to tell you if it will be cool enough on one pass, you will get close to your groundwater temp but usually not all the way there. You can do a test with boiling water and your hose water to make sure.
Things to look out for:
1. Make sure your wort and coolant water are running in opposite directions.
2. Don't run the wort full throttle in to the fermenter, choke the ball valve on your kettle down until you get the temps you want.