Is a fall on a wet deck covered by medical insurance or homeowners?

It depends on who fell and why. Homeowners Insurance is Property Insurance

Homeowners Insurance may sometimes provide a very small amount of coverage for minor household related injuries for the named insured.

Visitor injuries would be subject to home owners liability terms.

Major Medical insurance provides comprehensive coverage up to the policy limits regardless of where a personal injury occurred.

It's much better to handle it with your medical insurer.

Answer.homeowners