How to set up three separate networks?

[yky]

I have a duplex for rent. Duplex plus the main house would have a total of three networks. I would like to separate these three networks so people cannot peep into other people's data. What is the best way to do it and what is the most economical way of doing it?

The house has ADSL. So, I am talking about at least one modem and three routers.

 

[Alejandro85]

You certainly need 3 routers to be installed in each individual house. The LAN ports will go to every device for each individual network, while their respective WAN ports (often labeled as "internet") will be plugged into the modem LAN ports.

Note that this requires the modem to be in "router" mode, if available, and of course have at least 3 LAN ports. If that's not the case you probably need a fourth router to fix that gap. The houses' routers WANs will go into the LAN ports of the central router, whose WAN port will go to the modem, and the modem can be in "bridge" mode.
Another option is instead to use a cheaper switcher which will receive the WANs of house routers and keep the modem in "router" modem.

 

[yky]

Thanks for the reply.

The DSL modem has only two ports: Ethernet and USB. What do I do in this case?

 

[Alejandro85]

Then you need a fourth device, that can be either a switcher or another router.
With a switcher you put the modem in "router" mode and plug all routers WANs plus the single LAN modem's port into it
With a router the modem will be configured in "bridge" mode and you plug its WAN into the modem, and the individual routers WANs into the LAN ports.

This depends on if the modem supports router or bridge modes and how much do you want to spend on the extra hardware.