Fresh coconut and its water is short lived, it may last overnight in a cold fridge, but only if it goes straight in without delay or in the morning you will smell it, if you lack the sense of smell you will spit it out for the taste, if you lack both you will vomit, if your guts are iron, you will get sick.
We took water straight from the shell into a bottle on a 4hr hike in Malaysia, it was delicious but had to be discarded well before we finished, I now understand the great waste in that the water is tipped on the ground.
Even the milk is short lived and must be used immediately, I now understand why canned coconut is used in curries where fresh is plentiful.
Some advocate the milk can be fermented with kefir grain, others claim they ferment the water with tibicos, I have even seen coconut yogurt in supermarket, I do not think that is possible as in a warm situation it will rot before it can nicely ferment.
I have ordered the three, kefir grain tibicos grain and a so called coconut yogurt culture, when I stipulated fresh water, the lady said bottled, concerning milk she could not comment, concerning yogurt she said canned.
I love coconut and soon I will be testing it for myself, my girlfriend buys the milk and the grate fresh for curries, I cringe at the waste, liters upon liters a day tipped on the ground.
Traditionally it not heard of, research on prolonging its life naturally has been futile, traditionally the water is drunk or discarded and the meat used immediately.
Hopefully this is because coconuts are abundant year round and the ancients had no need to preserve it or dry it. Today we hate waste and may find the way.