Earlier quoted context omitted.
They do pay for it. Their use of water is profitable, for them. Whether it is profitable for society as a whole is a different question.
They barely pay for it. Most of the people holding these rights pay an absurd fraction of what a city-dweller would pay for the same amount. That's the only reason it's profitable for the farmer.
Water itself is ‘free’ until there is no more - minus the infrastructure costs to get it where you want of course, which can be zero to insanely expensive depending on the source of water.
City dwellers are paying for the infrastructure to get clean, drinkable water to their doorstep at precise pressures 24/7 + any payments to water source rights owners.
Farmers are paying for bulk delivery of massive quantities of non-potable/drinkable water to their fields during specific times of the year.
These are not comparable things at all.