If you search you will find a bunch of DIYs and how-tos about this.
I believe it's common to buy membrane wholesale from China
, and then "all you need to do" is pump water
into it at a certain pressure.
The part I've been unable to find is energy-recovery pumps at this scale.
If you use some random regular 12v water pump
you will consume at least, as I recollect, 2.5x as much power to pump
water through the system.
If you find suitable off-the-shelf energy-recovery pumps, I'd be very interested to hear about it.