Whenever I break coconut for the purpose of cooking or as native chicken feed, I always discard the water away. Why? Because old coconut water taste is inferior as compared with young coconut water. The same situation happen in most copra processing area. A lot of coconut liquid endosperm are wasted.
I grated some coconut for making suman, rice cake cooked in coconut milk. I saved the coconut water, filtered it using clean cheesecloth. I added some sugar to taste, (matured coconut water lacks sweetness). The result was great, the taste is like a mixture of young coconut water and virgin coconut oil.
Matured coconut water can also be used for making vinegar, wine and nata. As a medicine, it is used to cure and prevent renal disorders. Formation of renal stones can be avoided by drinking coconut water daily.