Fire hydrant being used by a business

When I walk my dog in the morning I have noticed a fire hydrant being used by a business. My estimate would be that I have seen them using the hydrant about two dozen times in the last five months, including three times in the last 7 days. The business is an arborist, with a business address 8 miles from the hydrant, and they are filling a tank on the back of a flat bed pickup truck. The pickup truck has company decals on the doors and the person doing it is wearing a t shirt with the same company name on it. I am not from Houston and this activity has struck me as unusual. I know I am being a busybody but is this normal here and should I care or does it not matter?