I'm curious about why plumbing codes (in locations different than mine) have some of the following requirements.

1. Accordion type flexible water line connections are not allowed. (As Steve Lavimoniere says in https://www.youtube.com/watch?v=UoMzdqO5AZU ) I don't know if this also applies to the pressure relief drain.

2. A vacuum breaker must be installed on the cold water line. (He says it keeps the tank from collapsing should the fire department start using a lot of water from the main iine - only a concern in big cities?)

3. A top-mounted factory installed "short stem" pressure relief valve must be replaced by a "long stem" pressure relief valve.

From other videos:

4. A service disconnect box is required. Romex cannot be used to connect the disconnect box to the heater. (In my location, the pros use a cable that resembles an appliance cord for a dryer or stove.)