Hi Garry,
That would be a bold move! Seeing as an RO requires a drain, the softeners require a drain and the carbon vessels require a drain I don't know why they couldn't just pop a floor drain in for you?
Where abouts would you place a leak detector - so many options to choose from?
Even when the plant isn't leaking it's nice to have somewhere to pour the water from the filter bowls or leave filters to dry/drain. Also comes in handy for when you need to get shut of your water sample for your hardness and chlorine checks.
When you get your carbon and softener re bedded in the future - the lack of a drain could prove a real headache!
Every plant needs a drain and a bund. But that's just my opinion.
I realise it doesn't really answer your question but thought I'd give some reasons why to argue for one.
Ian Wilde