What to do with water heater and water softner when draining water from plumbing?

Hello! I may have a problem with water hammer or pockets of air or whatever in my plumbing system. In order to troubleshoot, I want to drain the water from the pipes for the whole house and then refill it. What should I do with the water in water heater and water softner? Do I drain the water heater and water softner? Just turn power off on my Kenmore water softner? or use bypass valve? Thanks for your time!