In most reasonably-densely populated areas in the US, there will be municipal water systems for fresh water, and municipal sewer systems for drainage.
But in rural areas each home would have its own water source (well) and its own drainage (septic tank plus leach field, usually).
The septic tank is often not visible -- it would generally be dug to access every so often for cleanout. Its location would be known by the installer and hopefully by the homeowner, and location of the house plumbing could help locate it, but it's often covered over completely except while being serviced, so I doubt we could locate it from listing photos or google aerials. Let's just hope that LE inspected it.
MOO
That is the same as it is here then regarding septic tanks.
Did you happen to see any reports they had removed items from the house when they searched?
I'm flashing back to Gannon's case, a little child, also Colorado, they searched several times and then one night they returned and they removed a substantial quantity of items..
I checked how long that new listing had been active, 59 days, yesterday, 2 months. I'm unable to recall date of searches but it was longer than 2 months ago, I think.. I'm not sure because I was playing catchup and trying to read every thread one by one before my eyes failed me and I skipped over to Nancy Grace for a synopsis/shortcut but I know I missed tons.
I never came this late to a case before and reading all the posts was extremely enjoyable...no stones unturned...that's what is great about Websleuths.
It is good to see the house interior and to get a sense of who she was and how it might have been for her living there, so far from home...
My heart went out to her and the sense of profound grief was almost overwhelming.. I felt myself wanting to make it right for her, that those of us who live have a debt to those taken, to make things right on their behalf. Sorry for rambling and all wild speculation on my part.
Nobody will buy it, it's beautiful but it's not right or righted yet.