Help with water filters, please

[unblocktheplanet]

You could say I've lost the thread, ahem.

 

So kind bloke who's already done this gave me pointers to an RO system he uses at home. This one, joined with this one which still needs a post-carbon water filter plus UV for best results.

 

More questions. The first of these wants me to pick pipe diameter. How do I do this?

 

Which of these post-carbon filters fit best into the two above? And which UV filter?

 

It was mentioned that the UV filter needs to be on a separate switch. That sounds like manual turn on, turn off. And I'm the guy who loses the thread! Are there not UV systems which turn on when the water flows and off when it stops?

 

How much space does this set-up require? How much would a real plumber charge to set this up?

 

Thank you. Sorry to be so dense...