I live in Mexico, just 10 mins from the sea; A fresh-coconut paradise.
In spite of being easy to get fresh young (green) coconuts at many street-stationed vending karts, I saw a pile of (skinless) hairy cocnuts very unexpensive and bought 6 pieces;
I got home and opened all of them to store the water in the fridge, and avidly drank half a cup of healthy water..glub..glubb....YEEEIIIAACCKK!!!...-auto reverse flow response- WWWAAAHHHhh (vomiting)most of the water came out...
....IT WAS RANCID!!!...it gave me an acute headache and the runs for most of the night..
Now I know better....the rancid water comes from existing-oil oxidation and it is highly poisonous and really bad for your liver and kidneys....

It happens that the coconut meat and water are sealed protected from outside air and heat,by the hard shell,which becomes extremely fragile without the fibery cushion that naturally  forms around it..
The fiber is removed to gain space and be able to fit more nuts in a single load, but they are roughly treated along the way,some get tiny cracks letting air in, others receive direct sunlight and the heat breaks down the balance inside the 'nut' leaving just a few lucky ones, barely 'alive' to be of some good.

It is most likely you found one of these weird-tasting water, in the process to getting rancid.

The rancid flavor is very distinctive as it tastes like SOAP, and the meat looks 'eroded'.
This is due to the fact that after the oil in the water is 'consumed' by reacting with oxygen, it looks for extra 'fuel', in the form of oil in the white meat.
The reaction will continue until the oil is consumed, and the it will rot and escape   out in a gaseous form, leaving just a fetid stench behind..

Try whole 'encased' coconuts when possible, and if you're in a compromise , try weighing the coconut :
//too light=> DISCARD
+++feels heavy-> KEEP IT
+ not sure? then shake it close to your ear..  
** do you hear and feel liquid inside ?
// less than half full? -> DISCARD
++ about half full and above -> KEEP IT

I  hope it helps

Kind Regards