Note that sometimes when a coconut is young, it takes a few years for it to hold fruit that is useful for anything. Sometimes they will drop most of the flowers, then grow a few coconuts, then abort the coconuts before they are large enough to have any water or meat inside. Sometimes they might do this a few years in a row, before really getting established. Most do not produce at their peak rate for quite a number of years, so it can take them a little while to get going.
Just in case you did not know, the green coconuts produce meat in addition to coconut water to drink, and it is quite healthy. It's thin and in a more gelatinous state than typical mature coconut, and has all the electrolytes with only a fraction of the fat and calories of the mature version. It doesn't taste much like mature coconut though. I sometimes will have a whole green coconut as my breakfast. It's highly nutritious, and here it is free. Produces maybe about 1 cup of thin gelatinous nut meat, and 1-1.5 cups of coconut water. Coconut water tastes different depending on what tree it comes from. The trees in my yard produce the 2nd best coconut water I have ever tasted. The best was in another country and I can't get it again - but it tasted very nutty and fresh. Mine oddly tastes very sweet and slightly bland, like sugar water. My neighbors' coconuts vary, but none can compare to mine... most are tasteless, or even a bit unpleasant flavored. Hard to say if this is a nutritional thing, or by individual tree, or species. The Keys are prone to coconut mite, and I wonder too how this affects taste of the water. The meat too, of course, is variable. Mine have good meat, but not the best. Some others I've tried are bland, or taste kind of gross. Some of the coconuts I tasted in Central America had some of the best flavor I've ever had - much better than I thought coconut could taste. People tend to just think a coconut is a coconut, but like all other fruits, that is just not true. I have not identified what variety my trees are yet, but they don't appear to be much different from all the other trees around here.