no you dont need a permit for an RO system well not in the uk anyway.
You sure about that fella?
http://www.legislation.gov.uk/uksi/1999/1148/regulation/5/made
5.—(1) Subject to paragraph (2), any person who proposes to instal a water fitting in connection with any of the operations listed in the Table below–
(a)shall give notice to the water undertaker that he proposes to begin work;
(b)shall not begin that work without the consent of that undertaker which shall not be withheld unreasonably; and
(c)shall comply with any conditions to which the undertaker’s consent is subject.
TABLE1. The erection of a building or other structure, not being a pond or swimming pool.
2. The extension or alteration of a water system on any premises other than a house.
3. A material change of use of any premises.
4. The installation of–
(a)a bath having a capacity, as measured to the centre line of overflow, of more than 230 litres;
(b)a bidet with an ascending spray or flexible hose;
(c)a single shower unit (which may consist of one or more shower heads within a single unit), not being a drench shower installed for reasons of safety or health, connected directly or indirectly to a supply pipe which is of a type specified by the regulator;
(d)a pump or booster drawing more than 12 litres per minute, connected directly or indirectly to a supply pipe;
(e)a unit which incorporates reverse osmosis;
(f)a water treatment unit which produces a waste water discharge or which requires the use of water for regeneration or cleaning;
(g)a reduced pressure zone valve assembly or other mechanical device for protection against a fluid which is in fluid category 4 or 5;
(h)a garden watering system unless designed to be operated by hand; or
(i)any water system laid outside a building and either less than 750mm or more than 1350mm below ground level.
5. The construction of a pond or swimming pool with a capacity greater than 10,000 litres which is designed to be replenished by automatic means and is to be filled with water supplied by a water undertaker.
This is why I would keep quiet about it.
im sure about it.
if you need a permit for them the people selling them would have to tell you by law!
having our otherside of our business in the building trade we have done several of those things in that list and it all compleys and passed inspections with no problem,.
if you want to quote things how about this one then about being on a water metre??
(2) These Regulations do not apply to a water fitting installed or used, or to be installed or used, in connection with water supplied for purposes other than domestic or food production purposes, provided that–
(a)the water is metered; .
(b)the supply of the water is for a period not exceeding one month, or, with the written consent of the water undertaker, three months; and .
(c)no water can return through the meter to any pipe vested in a water undertaker.