Does it definitely charge or does it seek to look like it does, by offering a series of different options (that you arguably don't need) at cost, but still dispensing tap water for free?
The one at King's Cross is like that and I was surprised to see many people paying.
I can't quite remember but I think you pay for filtered water and flavours, or even CO2, and it really does push them so you don't notice the free option.
A bit like free museums that pretend there's an entry fee by making signs with suggested donations look like price lists.