Unfortunately, there is no perfect lock. All locks have some way of being cut, picked or destroyed.
U locks and Shackle (folding) locks are reliable and require more power and larger tools to defeat. These are the optimal choice for theft prevention.
A cable lock should only be used as a secondary means of protection. You should not rely on a cable lock for security. These are often targeted by thieves who carry tools specifically to defeat these locks.
While the water meter behind the grocer may seem like a good idea, the best locations are places where the bike is well-lit and visible.
Make sure to lock up to a post or rack which is securely fastened. A thief will not think twice to cut a rack or fence to get to your bike.
Ideally, you should lock up both wheels.
Using two locks is recommended for overnight stays or unsupervised work parking.
Give it a shake. Pull on the lock.
Try to look at it from a thief's point of view: Is the anchor post secure? Is the lock reliable and around the proper areas?
It is always a good idea to take any visible electronic accessories with you when stowing the bike publicly. Lights are easy targets.
Take care not to leave any valuable items in your bags as they may be subject to rummaging by desperate thieves.