Can a WS355 be installed in a flat / apartment?

I wonder what a WS355 is. Oh, look. Its a water softener. Nice of you to give us that clue.

Manual here:

http://www.bwt-uk.co.uk/en/business/products/Pages/DownloadManual.aspx

Overflow will go through the wall to the outside world

Drain would probably go to the same drain as your washing machine.

Why not contact the maker for their advice, instead of asking here?

XXX
August 2016