is it illegal to re label a product and resell it?

is it illegal to re label a product and resell it, for example u buy bottles of water from xyz company, you rip the label off and put your own brand name abc company, and sell it to the public. you really dont change any of the facts on the bottle for example contents on the first label were H2o then thats the same that will be printed on your label. is this illegal?

TIA
if so can you explain why?