That's what I was thinking but my water bill is never more than P100-150/month. I don't see any water seeping out from anywhere either (it's gotta go somewhere right? Maybe there's a massive sinkhole forming under the house. Good thing I rent. lol). I think that the pump/tank might not be very well isolated to just my house, there is a chance that it could be feeding the 3rd (and very large) tank, the apartments and another house on the property. Oh well, I have water now, best to quit while I'm ahead.
Pool filter type sand trap might keep rocks out of your pipe. I would probably prefer a wye strainer. for a 1" pipe going in a 3" wye strainer should be more than sufficient. The wye strainer needs to be larger than the line so the flow can slow down and give the rocks time to settle out to be caught by the strainer, which can have a simple ball valve on the lower part where you can let the rocks out every month or so.
