Flow reducer usually comes matched with your RO unit. I say usually, as just foundWhere would we find a flow reducer ian?
Reverse Osmosis Consumables - Flow Restrictors - Osmotics Water Filtration
Also if fitting an RO unit, get an auto shutoff valve. http://www.osmotics.co.uk/products/Auto-Shutoff-Kit-with-Float-Valve.html
See here Installing an Auto Shut Off Valve - Instructions - Bulk Reef Supply how they work.
This enables you to have the RO unit permanently connected to mains water (except via maintenance isolating valves), you just turn on your RO output valve, in the shed in my mates case say 20m away, and it opens the water in and RO water flows.
Also auto flush units are useful as some cheap RO units require you to disconnect the outlet pipe to flush the unit. Basically you remove the flow reducer to allow full pressure water to flow through for a minute or two every so many hours of operation.
Look auto flush units as well.
Auto Flush Solenoid Valve - Osmotics Water Filtration
Still in use once a week. Still "twitchy" though about having mains pressurised hose pipe in the lounge near TV, sat box etc. But really save time for a 90litre water change.like your auto heating water butt