Thank you for the additional information:
"However, it would not be reasonable to sue him for the damage to the pool since you have concluded that his pressure washing the pool to get it ready for plastering was not the only cause for the damage, that you had agreed that severe rainstorm contributed to the damage. So, you are very limited to what you can sue him for."
Really the pressure washing is more of a side note. It's the fact that he drained the pool completely and apparently without taking proper precaution in preventing it from floating up and cracking. Had he not drained the pool when he did and also taken the proper precautions (like weighing down or releasing the hydrostatic valve on the pool or partially filling it knowing that a rain storm was coming), the rainstorm would not have had the effect that it did. Does that not constitute some sort of negligence on his part? Why would I be liable for the repairs to the pool? Doesn't he have at least some sort of liability in this situation?
Response: My response was based on your initial post. Since you have added information that was not part of your initial post, I will amend my response accordingly:
Does that not constitute some sort of negligence on his part?
Response 1: Yes, it does.
Why would I be liable for the repairs to the pool?
Response 2: You would NOT be based on the information that you have added. You would sue the contractor for the damage to the pool plus the return of your deposit. So, you would need to get a written estimate from another contractor as to how much the repair would cost.
Doesn't he have at least some sort of liability in this situation?
Response 3: He does.