OK, time for a little history here ...
(and I'll try not to garble it up this time!
We used to make pools out of concrete, and our pipes were metal. No problems.
Then we started making our pools out of metal that was wrapped in plastic - effectively insulating the shell - and the pipes out of plastic. People started getting tingles when they sat on the deck and dangled their legs in the water. Amazingly enough, this problem only happened with the fresh water filled pools.
Wherever the electricity comes from, it was felt that the solution was to bond everything together to a ridiculous degree. Along cane this 'equipotential plane' and even a requirement to 'bond' the water.
Code requirements seesawed back and forth; I think the latest version has returned to specifying a copper grid, in preference to just ordinary rebar. I might be a bit off - perhaps the copper is only called for if there's no concrete deck. Apparently the copper wire that goes around the pool, bonding the shell in four places, isn't enough.
As for bonding the water ... if you don't have metal pipe to bond to, there are a variety of metal gizmos made to help you do this.
The entire purpose of all this is to make sure the ground around the pool is at the same exact potential as the water inside the pool.