When it comes to septic systems, there are two main types you'll hear about: conventional (anaerobic) and aerobic. If you're building a new home, replacing a failing system, or just trying to understand what's in your yard, knowing the difference matters — because the wrong system for your property can mean years of problems and thousands of dollars in avoidable costs.
How a Conventional System Works
A conventional septic system is the simpler of the two. Wastewater flows from your house into a buried tank, where solids settle to the bottom and bacteria break them down without oxygen (that's what "anaerobic" means). The liquid effluent then flows out to a drain field — a series of perforated pipes in gravel trenches — where the soil does the final filtering before the water reaches the groundwater.
Conventional systems have been around for decades. They're reliable, relatively affordable, and require minimal maintenance beyond regular pumping every 3 to 5 years.
Pros of Conventional Systems
- Lower upfront cost (typically $5,000 to $10,000 for installation)
- Simple design with fewer mechanical parts
- No electricity required to operate
- Lower ongoing maintenance costs
- No required maintenance contract
Cons of Conventional Systems
- Requires suitable soil for the drain field (good percolation)
- Needs more land area for the drain field
- Not an option on rocky, shallow, or poorly draining soil
- Effluent is less treated before reaching the soil
How an Aerobic System Works
An aerobic treatment unit (ATU) adds a critical step: it pumps air into the treatment chamber, creating an oxygen-rich environment. This supports a different — and much more aggressive — type of bacteria that breaks down waste faster and more completely than their anaerobic cousins.
The result is a much cleaner effluent. So clean, in fact, that some aerobic systems can use spray heads to distribute the treated water across your yard instead of relying on a traditional drain field. This makes aerobic systems the go-to choice when soil conditions or lot size rule out a conventional system.
Pros of Aerobic Systems
- Works on properties with poor soil, shallow bedrock, or small lots
- Produces significantly cleaner effluent
- Smaller footprint — no large drain field needed
- Often the only permitted option in the Hill Country
- Can use spray distribution instead of drain field
Cons of Aerobic Systems
- Higher upfront cost (typically $12,000 to $20,000+)
- Requires electricity to run the aerator and pump
- More mechanical components that can fail
- TCEQ requires a maintenance contract with a licensed provider
- Maintenance inspections required every 4 months
What Determines Which System You Need?
In a perfect world, you'd get to choose. In reality, your property usually makes the decision for you. Here are the main factors:
Soil type and percolation rate. A perc test tells us how fast water drains through your soil. If it's too fast or too slow, a conventional drain field won't work properly, and you'll need an aerobic system.
Depth to bedrock. Here in the Hill Country, it's common to hit limestone just a few feet down. If there isn't enough soil depth for a conventional drain field to do its filtering job, an aerobic system with spray distribution is the answer.
Lot size. Conventional drain fields need room. On smaller properties, there may not be enough space for the drain field plus the required setbacks from wells, property lines, and structures. Aerobic systems need less real estate.
County regulations. Both Comal County and Hays County follow TCEQ (Texas Commission on Environmental Quality) rules for on-site sewage facilities. The county's designated representative evaluates your site and determines what's permitted. In many Hill Country locations, the soil and terrain simply don't allow a conventional system.
Our Recommendation
We install both types of systems, and we'll always recommend what's right for your specific property — not what's most expensive. If your land supports a conventional system and your budget prefers it, that's what we'll build. If the soil or lot size says aerobic, we'll explain exactly why and walk you through what to expect.
Either way, you'll get a system that's properly engineered, permitted, and built to last. That's what matters most.
Need help with your septic system?
Start your project or call (830) 837-0050