Oh dear it seems that Stuart has deleted himself from the forum. That's a real shame, I had not meant any offense whatsoever.
For anyone who is interested, the regulations regarding water installations are
HERENotice the table in section 5, part 4(e) "a unit which incorporates reverse osmosis"
The reason they don't apply to the vast majority of pole users is simple.
Most pole users use a van-mounted system where the RO units are in the van. These are not an installation in a dwelling, therefore are not under the regs.
Although the regs do apply to static systems, most window cleaners do not "install" the system, they simply attach it to the water supply when needed. This way, the RO unit is an appliance, not an "installation"
However, if you do have your system plumbed in, and it is genuinely an installation, you should get a permit.
-Philip