People used to live next to cemeteries and drink well water.

Yes, they also got very sick from doing this.

How were any houses originally built?

Well, sometimes they were just built.

It's a good thing we've learned a few things since then. Not that city planning is perfect. Far from it. But it certainly does serve a purpose.

Used to be that an acre of land generally had enough space for a proper septic tank and drain field. But I think in some places it is a little higher now. Depends a lot on local geography of course.

It depends on the area. In Michigan, for example, the area here is mostly swampland, houses with no infrastructure have to build their own. Usually that means running new power lines, and figuring out well water and septic. Septic is trickier than it seems, you need to have enough space for a leech field large enough to drain properly, it needs to flow properly (away from your home, away from your own well) and soil absorption has to be high enough (and the water line low enough) to handle it all. Having a lot of land isn't enough on it's own, it has to have enough natural drainage to be able to handle itself and anything you need to seep into it.

For example, you might have an acre of land, but if too much of the soil underneath is clay, or if the water table is too high, the wastewater might not drain fast enough, so it sits and stagnates or mixes with freshwater, despite having "lots of land". You generally need a surveyor to produce and sign off on a Topographical Survey to assess that.

So yeah, "there were no sewers once upon a time", sure. But if you try to build suburban-like densities out here without a solid plan signed off, you are likely to end up piping your own sewage right into your own water taps.

https://www.miottawa.org/Health/OCHD/pdf/AboutSewage.pdf