Yes, bad coconut water will make you sick. It is important to get fresh coconut water because if coconut water has any off colors or flavors, that generally means it is contaminated with harmful bacteria and/or mold. Consuming contaminated coconut water can cause upset stomach, diarrhea, and allergic reactions. Coconut water should be kept refrigerated and will stay good that way for approximately one week. For longer term storage, you can freeze your coconut water. Allow it to defrost fully then mix before consuming after being frozen, as the natural sugar it contains won't be distributed evenly otherwise.