The job a toilet system does
Human waste carries pathogens: germs that cause disease. A toilet system has one main job: keep those germs away from people, food and water.
In a town, a sewer does that for you. On most rural land, you are responsible for it yourself.
Blackwater is wastewater from toilets. Greywater is wastewater from sinks, showers and laundry, as in lesson 19. Many rules treat the two very differently.
A failing system can contaminate wells, streams and neighbors’ water. That is why this topic is closely regulated almost everywhere.
How a septic system works
A septic system is an on-site system that treats household wastewater underground. A conventional system has two main parts (EPA):
- A septic tank: a buried watertight tank. Solids settle to the bottom as sludge. Grease and light material float to the top as scum. Bacteria break some of it down.
- A drain field, also called a soil absorption field: a set of buried pipes or chambers in gravel or soil. Liquid from the tank seeps out, and the soil filters and treats it.
The soil does most of the treatment. That is why a site evaluation, often including a percolation test of how fast water soaks into the soil, comes before any design. Some sites need more complex systems that cost more and use more power.
Text description
A simplified, not-to-scale section through the ground. All household wastewater flows from the house through a pipe into a buried, watertight septic tank. Inside the tank, grease and light material float to the top as scum, solids settle to the bottom as sludge, and bacteria break some of it down. Access lids reach the surface for pumping and inspection. Liquid from the middle of the tank flows on to the drain field: buried pipes in gravel trenches. The liquid seeps out and down, and the soil filters and treats it. Cars, buildings and trees should stay off the drain field. Notes say to have the system inspected at least every 3 years and pumped typically every 3 to 5 years, and that site evaluation, design, setbacks and installation are for a licensed professional with a permit.
Living with a septic system
A septic system can last for decades with care, or fail early without it. EPA’s SepticSmart guidance says:
- Have it inspected at least every 3 years by a septic professional. Systems with pumps or other mechanical parts need a check about once a year.
- Have the tank pumped, typically every 3 to 5 years. How often depends on tank size, household size and water use.
- Use water efficiently. Too much water at once can flood the drain field.
- Flush only toilet paper. Wipes, grease, medicines and chemicals harm the system.
- Do not drive, park or build on the drain field, and keep trees away from it.
A septic system is often one of the larger single costs on a rural site. Costs vary widely with soil, site and local rules, so get local quotes.
Composting toilets
A composting toilet breaks down human waste with little or no water, using air, time and a dry cover material like sawdust, wood shavings or peat. It can be a built-in unit or a simpler bucket-and-bin system.
Many composting toilets use urine diversion: urine goes to a separate container or drain. That keeps the solids drier, which cuts odor and helps them break down.
The result is not ready to use right away. It needs time in a finishing stage to reduce germs, often a year or more, and longer in cool climates. Many states require the finished material to be buried or taken away by a licensed hauler (EPA). Keep it away from food crops unless your local rules clearly allow it.
What a composting toilet does not solve
A composting toilet removes toilet water. It does not remove the rest of your wastewater.
- You still have greywater from sinks, showers and laundry. Many places still require an approved way to handle it, and some require a full septic system anyway.
- Urine, if diverted, needs a lawful destination.
- Many jurisdictions only approve composting toilets that are certified to a recognized standard. Home-built systems may not be allowed as the main toilet.
Ask your local health department before you plan around one. Rules vary more on this topic than on almost any other in this course.
Text description
A flow diagram in three rows. Top row, solids: the composting toilet sends solids, with a dry cover material such as sawdust after each use, into a composting chamber with air and a vent. The material then goes to a finishing stage of a year or more, longer in cool climates, to reduce germs. Finished material is buried or taken by a licensed hauler, as local rules allow, and kept away from food crops unless rules clearly allow it. Middle row, urine: urine diversion sends urine to a separate container or drain, which needs a lawful destination. Bottom row, greywater: sinks, the shower and laundry still make greywater, which needs an approved greywater or septic system. A note says the local health department decides which of these paths are allowed.
The toilet smells
“Our composting toilet smells strongly of ammonia and sewage, and the bin looks wet and sticky.”
Clues
- The family added two more people for the summer.
What is the most likely cause?
Compare the options
Pros, permits and risks
Untreated sewage can spread disease and contaminate drinking water. A failing drain field can pollute a well, especially one that is close by or shallow (EPA). Local rules set minimum setback distances between septic parts, wells, streams and property lines.
Check
You install a composting toilet. What still needs a plan?
Summary
- Toilet systems keep pathogens away from people and water.
- A septic system settles solids in a tank and treats liquid in a drain field. It needs inspections and pumping.
- A composting toilet saves water but needs care, and greywater still needs a plan.
- Both are permit topics. Start with your local health department.
Next, you will look at compost from the kitchen and garden.
Go deeper: why soil matters so much
In a septic drain field, the soil does the treatment. Soil that drains too fast, like coarse gravel, can pass germs to groundwater before they are filtered. Soil that drains too slowly, like heavy clay, or a high water table, can make wastewater pond on the surface. That is why the same house can need a simple system on one lot and a complex, more costly one on the next. Septic design is licensed work in most places. This course explains the ideas only.