Hello people;; Recently $800,000 has changed hands w/ the sale of two houses in
My rural neighborhood. My question would be, is the guy (me) that
Keeps the water tank full including meeting state standards, entitled
To a check? I've been at this for "free" since 1980, and it is grating
On my head.

I'd stop doing it for free for one thing...

I assume that they don't chain you to the valves and hold you captive while you keep the plant running with the allowed standards. If you were a paid operator, you wouldn't be entitled to a share of anybody's sale of a home and since you are doing the job for no compensation, you still aren't so entitled.
Are you certified to do water quality testing? Who reviews your work? Give the authorities notice that they need to hire someone and apply if you meet the qualifications. I personally would not care to have my water quality controlled by volunteers. Is this in the U.S.