Bathroom zones are just a way of telling which extractor fan you can install at a specific place. See the image below.
Suitable for IP68 (submersible to 9m) Water light fittings, suitable for saunas, steam rooms or underwater.
Suitable for IP65 (Jetproof) Fitted where a jet or stream of water is present, for example from a shower handset.
Suitable for IP44 (Splashproof) Should be fitted whereever splashing may occur. Fitted within 0.6m of a basin or other water source.
No splashes or water jets will occur
Bathroom Zones for extractor fans