Its not advisable to use water direct from outside main immediately to your water heater storage tank.

This is because in the event of water disruption, and you accidentally left the heater turned on, the heater unit would overheat and you would end up with a burned fuse...which costs RM100+ to replace (price inclusive of water heater tech installer)

From my point of view, both your plans: A & B will work. Depends on how much work it is to create additional piping + expenses if you decide to go with B.

Ultimately you'll have to weigh the pro and cons yourself (cost, hardship, mess, etc)