If this is true, why is it illegal to build anything but low density suburbia in most places?
I grew up just outside a decent-sized city in Canada, now living in Texas...both places, on septic. Its not rare.
I live on 3.5 acres and have a water treatment system and part of the reason is that there's a shortage of homes I _actually_ wanted, which are decent flats in the city where my kids can bike to school, so they're very expensive.