Coconut water ..

Okay i know this has nothing to with post partum but yesterday I witness a lady mixing formula with coconut water instead of regular water for her baby i would she might 3 or 5 months give or take.. then 2 hours later gave her coconut water.. and she had diarriah.. any who .. is it safe to give coconut water or mix coconut water with formula.. im confuse .. i know you can give a baby coconut water until they eat solid foods right ?!. Has anyone witness anything like that..