Buying RO / DI - I know nothing

[Snaz]

My folks will be buying an all in one Nano in the near future and the subject of water came up. I think we are going to install for them an RO/DI unit as they are already buying bottled spring water and an RO/DI unit will fill both roles, great drinking water and great reef water.

I know the concepts of RO/DI filtration but I do not know the name brands or setup or costs so any help would be appreciated. Their tank will probably be 32 gallons or less and so weekly water changes would be around 3 gallons. They drink on average 6 gallons a week(one 20 litre bottle) for a total of less than 10 gallons a week.

I originally thought of installing in the laundry room of the basement but the thought of them dragging the water up the stairs has me thinking installing on the main floor a better idea, maybe under the kitchen sink?

Where do I start for my research? What brands should I be looking at? Thanks much.