No it does not need to be installed under your sink. But you do need a little bit of plumbing knowledge. There is a comprehensive guide included. You will have to plumb into the cold water pipe after the shutoff below your laundry sink. The drain you could just put into the laundry sink or the washer standpipe, securely fastened.
Yes, I would use a DI unit in Vancouver. I use one in Surrey, we get the water from the same source, don't we?
This is just one co. that has extras. you will need a housing
http://filterdirect.com/product_info...roducts_id=153
and a refillable DI cartridge to put into it and some plumbing fixtures to add the unit to the waterridge system.
The WR system also comes with a faucet for drinking water that you can attach, I guess to your laundry tub, or just do not use it. The tank, you could just put below the sink.