Water Deregulation - Small Businesses

Not sure if I'm allowed to ask for advice for a small business here or whether you only cover domestic. so please delete if not allowed.

I understand from 2017, water is now partially deregulated, and a small business can now switch water suppliers just like everyone can switch gas and electricity? (but domestic users still can't switch). Is this true?

If so, my next question is, is it worth looking at switching water supplier?
Our existing water supplier is offering some discount if we sign to a 12 month contract with them, but should we shop around first?

Our existing supplier also say it's not worth shopping around, as at present the suppliers are restricted to a very small margin between the wholesale buying price and retail selling price, so no other supplier can offer any better price.

Any advice welcome