Have 3 machines on 1 wire

In the laundry room, I currently have 1 socket, with 1 underlying wire of 1.5 mm2 of section. This connects to a 16A circuit breaker. In the country I live in, voltage is 230V.

I need to install 3 machines in this laundry room:

• washing machine : 2100 W
• dryer : 2700 W
• tank water heater : 2000 W

This is obviously way too much for this 1 wire. The ideal solution would be to get a new wire from the fusebox, but that is hard to do, and would require redecorating large portions of the house, which I just can’t do at the moment.

So I thought of a solution. Could I replace the wire that currently goes from the fusebox to the socket, and replacing it by say a 4mm2 one?

I would put 3 sockets with this underlying 4mm2 wire, and plug the 3 machines on these sockets.

So 2 questions:

1. I read online that the tank water heater should be on its own wire, so that would not be the case in my scenario. Why do they suggest that, and is it somewhat reasonable to not follow this direction ?
2. Knowing that there are about 6m between the fusebox and the socket, how easy would it be for someone with no experience at all to to replace the existing cable by a new one, thicker?