I actually don't think they should've fired water cannon at it. just get a few more ships and block the entrance even more fully. What can they do?
But the idea that America would defend Philippines over a dispute over reef is laughable.
Doesn't matter if China fired a water cannon or not.
It is abundantly clear that the US has gained complete control of Philippines. What's happening now is that the US and the Philippine's elites are manufacturing consent with the PH public to fully, visibly, align with the US without causing internal opposition.
After all, what can internal PH sceptics of the US even do that would matter if they would be immediately branded traitors for supporting China against PH rights?
So that's the US game right here. Top-level decision for PH to fully support (or fall on its sword trying to serve) the US has already been taken, what's happening now its just the necessary manufacturing consent PR
Water cannon or not, PH would just do another thing to cross China, provoke a response, and then do internal manufacturing consent on its public against China.
I consider PH a lost cause for China (was never in contention anyway)