You had a 50/50 chance… Airborne transmission is one of the common methods which the virus is able to spread. Another method is through contact with surfaces, such as railings, equipment, sharing of masks, snorkels, regulators and touching areas around your face after having contact with an infected surface.

You should follow CDC as well as local requirements and laws. Lean towards the more conservative.

If one diver is not breathing from their regulator and is in close contact with their buddy, they are exposed to the exhalation from the buddy with the regulator in their mouth. Both divers are recommended to be wearing their mask and breathing from a regulator when performing buddy checks in close contact. The alternative is to walk through the steps, orally and watching the buddy perform the check on their own gear. If contact is to be made, it is recommended the diver sanitize after contact..

Sanitizing before setting up your gear helps reduce transmission from the gear to you and your to your gear.
After touching gear underwater because there is not enough information about the survival of the virus underwater. If in doubt, Sanitize
If you must touch your face or areas around your face, sanitize before doing so.
Sneezing or coughing. Try and move downwind from everyone and face away. Use the bend of your elbow to cough or sneeze into following by sanitizing
Touching high contact surfaces such as ladders, support structure, dive bench are area which see a lot of traffic.
Regularly through out the day makes sense. Contact with the virus can come from many places

Sunlight is not always an option as well as there is not enough information to support immersion in salt water will sanitize the area while viral killing disinfectants have been available and in use in hospitals, food and the dive industry for sometime and are proven to be effective, disinfectant is the best answer.

If you have placed the alternate air source in your mouth to test breath the alternate air source should be re-sanitized before the dive. Recommendation is to press the purge, with your buddy watching to verify gas is being delivered.

alcohol-based hand sanitizers are incompatible with compressed gas, especially oxygen-enriched gas.

If alcohol-based hand sanitizers are used before filling cylinders, ensure hands are completely dry and all alcohol has evaporated.

Try not to expose area where transmission is possible. Avoiding contact with first stage inlets, valve openings and fill whip openings reduces the chances of virus’ from being introduced into the tank or transferred through the regulator.

It is recommended that only store staff handle rental equipment minimizes equipment contact. Staff should be familiar with proper handling and sanitation. Before you handle/use the equipment it should be sanitized before and again sanitized after use.

There are many places which may be touched by divers. Hand rails, support posts, doors(hatches), seats, lighting, hangars, toilet area, wetsuits are a few examples.