How do I know what my water table is?
I would 1) ask your local Building Code office, or 2) ask your local public utilities office (particularly your plumbing inspector), or 3) ask your public works director, (i.e.: local Building project like a sewage treatment facility will have a Geotech report that will give you the water table...for the area where the facility is being built,) or 4) call local architects, or 5) call local CIVIL engineers, or 6) call DEQ office (especially if they issue drain field permits,) or 7) excavation contractors that specialize in the installation of underground utilities, or 8) hire a Geotech engineer. 

A Geotech engineer is very expensive. I'd call all the above before I spent a bunch of money on their tests and report. (Where I live, it costs about $4000.)