About 21% of American homes are on septic, including a majority of rural homes in Tennessee and a third or more of New Mexico homes. The rest are on municipal sewer. If you have a choice (rare on most properties — your home is generally on whichever system is available), or if you're comparing properties, the math is more nuanced than the convenience of "set it and forget it."
Cost comparison over 30 years
Sewer
Monthly sewer bill in Tennessee runs $25-$60; in New Mexico it runs $30-$70. At $40/month average, that's $480/year, $14,400 over 30 years. Plus connection fees if you're tying in for the first time ($3,000-$15,000). Plus periodic main-line repairs that the city handles via your taxes and rate increases.
Septic
Pumping every 3-5 years at $400 average = $80-$130/year, or $2,400-$4,000 over 30 years. Plus probable drain field replacement once over 30 years ($5,000-$15,000). Plus possible tank replacement ($4,000-$8,000) if it's not concrete or wasn't well-maintained. Total over 30 years: $11,400-$27,000.
Septic is comparable in lifetime cost to sewer in many cases, with the difference being where the money goes — sewer is steady monthly payments to a utility; septic is intermittent larger payments to contractors with long stretches of $0.
Maintenance and responsibility
Sewer
- Pay the bill, that's it
- Anything past the property line is the city's problem
- No tank to pump, no field to worry about
- No alarm to listen for, no permit when you renovate
Septic
- Track pumping schedule and arrange service
- Watch for warning signs (smell, slow drains, surfacing water)
- Don't flush wipes or pour grease
- Permit needed for additions that change bedroom count
- Inspection at sale (lender may require it)
- Be aware of the field location (don't pave, build, or plant trees over it)
Resale value impact
In rural markets — most of TN outside the urban cores, almost all of NM outside ABQ and Santa Fe — septic is the norm and doesn't hurt value. Buyers expect it. In suburban and urban markets, sewer is preferred and septic on a property within reach of municipal sewer lines is sometimes seen as a negative.
What hurts value reliably: a septic system in poor condition. Pre-sale inspections that come back clean cost $300-$650 and protect resale value substantially.
Failure modes and consequences
Sewer
Backups happen, usually due to clogs in your service line (your responsibility) or main-line backups (city's responsibility). Plumber visit ~$200-$500. Rare.
Septic
Backups happen from full tank ($300-$650 emergency pump-out), saturated drain field (much more expensive), or pump failure on aerobic systems ($700-$1,500). More common than sewer backups, and the consequences scale with how long they're ignored.
Environmental considerations
Both systems can be environmentally fine when maintained. Failed septic systems can contaminate groundwater and surface water; failed municipal sewer systems do the same at larger scale (sewer overflows during rainstorms are common in many cities). On a per-household basis, well-maintained septic is competitive environmentally.