Need some facts sorting out here!
In the UK you can order tap water (ie from the water supply!), or there will be a jug on the table for you to help yourself - for which there is no charge, but they don't usually put a lemon slice with tap water, just ice.
Or you can order mineral/spring water for which there is a charge, and you can ask for lemon with it.
Will this guys water have been free or would he have already paid for it anyway? Or did they 'upgrade' the 'plain water' bill to 'lemonade' (in which case, he may actually have only been charged a few cents for the sweeteners)
If he'd already paid for the water, that's mean to charge him for making lemonade. However if the water was free, I might call him a cheapskate but still wouldn't charge him - bad business sense if it's the usual thing to do there. Plus, how many people get refunds for not using sweeteners?!
"The customer is always right, even when they're wrong" and all that...
In the states resturants do not charge you for tap water, or lemon wedges. A few places will charge for lemon wedges but they list it in the menu pricing. This man was charged for a lemonade because he ordered a tap water with his meal, the water came with lemon wedges, normally the resturant would not charge you for this, however the owner observed that the man squeezed his 2 tiny lemon wedges and added some sweetner that is already on the table along with the other condiments, this caused the owner to charge the man for a lemonade at full price even though the man did not order a fountain drink. That's a problem, imo the only cheep skate here is the resturant owner.