DEFRA (Department for Environment, Food and Rural Affairs) are responsible for water policies in the UK, and not the water companies. Lets break things down and see where hot tub and swim spa owners stand when it comes to hosepipe bans.
DEFRA have agreed in writing with the hot tub industry (BISHTA), that hot tubs are not affected by hosepipe bans and can be filled or topped up as normal.
Swimspas/Exercise Pools are included in the same category as swimming pools. During a hosepipe ban, it is permissible to fill a brand new pool to save damage, but you are not allowed to top up or change the water in existing swimspas/exercise pools, except using a bucket or watering can.
The hot tub end is treated the same as a standalone hot tub and can be filled and topped up during a hosepipe ban.
The swim end must be treated like a swimming pool and cannot be filled or topped up unless it is brand new and just constructed or by using a bucket or watering can.
If the drought gets worse and a 'Drought Order' is applied, then at this point, you cannot fill or top up a hot tub with a hosepipe. However, you can use a bucket or watering can.