Do I have a good slip and fall case?

You could possibly have a case but you need to prove either actual or constructive notice to the grocery store. Water is pretty difficult to prove the length of time it had been on the floor. Merely because the accident happened there does not mean the grocery store is responsible. You have to prove they either knew about the water (actual notice) and failed to promptly clean it up, or prove that they should have known about the water in the exercise of due care (constructive notice) and failed to clean it up or post warnings. If it was readily observable by a cashier, for example, that may be sufficient to at least get to a jury on the constructive notice issue. I am currently handling a case against a local grocery chain for water on the floor, but when they helped my client up off the floor, the employee apologized and said they should have done something about the leaking fountain. In that case, they had actual notice.