What Is a Sewer System? Types, Components and Maintenance

A sewer system is the network of pipes, pumps and treatment facilities that carries wastewater away from buildings and cleans it before it’s released or reused. In San Jose and much of the South Bay, every sink, shower, toilet and washing machine drains through your lateral and city mains to the San Jose-Santa Clara Regional Wastewater Facility.

Rainwater travels separately, through storm drains to local creeks and the Bay. Sewer systems come in several types (sanitary, storm, combined, overhead, and vacuum, effluent and pressure systems), each built for different water and ground conditions. Whatever the type, they rely on the same parts: pipes and laterals, manholes, pump stations, force mains and treatment plants. Keeping them working takes routine inspection, cleaning, grease control and root management, on the public side by the city and on your side of the property line by you.

What Is the Difference Between Sewer, Sewage, Sewerage, and Wastewater?

A sewer is the pipe that carries waste; sewage is the waste and dirty water moving through it. Sewerage is the whole network that collects and carries sewage, and wastewater is any water that’s been used in a home, business or industry. A drain is the pipe that collects water from one fixture or place and leads it to the sewer.

Is Wastewater the Same as Sewage?

Not always. Wastewater is the broad term for used water from sinks, showers, washing machines, businesses and industrial processes. Sewage is the part of it that contains human waste from toilets. The difference matters because different wastewater carries different pollutants and may need different treatment. All sewage is wastewater, but not all wastewater is sewage.

How Do Sewers and Drains Differ?

A drain serves one place: a sink, shower, toilet, roof or street inlet. A sewer collects from many drains and properties and carries the flow toward treatment. Inside your home, the fixture drains join the building drain, which leaves the house as the building sewer, or lateral, and connects to the public sewer main.

What Are the Main Components of a Sewer System?

A sewer system has five main parts that move wastewater from its source through collection and treatment to discharge.

Sewer pipes and laterals. The lateral is the private pipe from your house to the public main, usually with a cleanout where it can be reached for cleaning. Mains run under streets and get larger as they join, carrying flow by gravity at a continuous downward slope. Older South Bay laterals are often vitrified clay or cast iron; newer ones are PVC or ABS. San Jose alone cleans and maintains over 2,000 miles of sewers.

Manholes and access points. Vertical shafts at junctions, changes in direction or slope, and along long runs give crews access to the mains for camera inspections, cleaning and clearing blockages. Cleanouts do the same job for a home’s lateral.

Pump stations and interceptors. Where the ground is too flat or the flow has to go uphill, lift stations pump wastewater to a higher point so gravity can take over again. Large trunk sewers called interceptors collect flow from many neighborhoods and carry it to the treatment plant.

Force mains and pressure pipelines. These sealed pipes carry wastewater under pump pressure from a lift station to a gravity sewer or the plant. Air-release, check and isolation valves control pressure and prevent backflow.

Treatment plants and outfalls. The plant removes solids, organic matter, nutrients and harmful organisms, then releases the treated water through an outfall or sends it for reuse. The solids are processed separately.

What Are the Different Types of Sewer Systems?

The main types are sanitary, storm, combined and overhead sewers, plus alternative systems for places where gravity sewers don’t work. They differ mainly in what water they carry and how they move it.

Sanitary Sewer System

A sanitary sewer carries wastewater from toilets, sinks, showers and appliances (both “blackwater” and “greywater”) from homes and businesses to a treatment plant. It’s kept separate from rainwater. Most of it flows by gravity, with pump stations where the slope isn’t enough. San Jose’s sanitary sewers carry the city’s wastewater to the Regional Wastewater Facility.

Storm Sewer System

A storm sewer carries rain and runoff from streets, roofs, sidewalks and parking lots to creeks, rivers and the Bay to reduce flooding. It uses gutters, catch basins, inlets, culverts and large pipes sized for storm flows. In San Jose the storm drain system carries runoff, untreated, to the nearest creek or waterway, so nothing but rain should go down a storm drain.

Storm Sewer vs. Sanitary Sewer

A storm sewer carries rainwater and runoff; a sanitary sewer carries sewage to treatment. Keeping them separate keeps rainwater from overloading the treatment plant, and keeps sewage out of creeks. That’s why downspouts and yard drains must never be connected to the sanitary sewer.

Combined Sewer System

A combined sewer carries sewage and stormwater in the same pipes to a treatment plant. In heavy rain the flow can exceed the system’s capacity, and the excess may be released through overflow points as a combined sewer overflow (CSO) of untreated sewage and stormwater. Cities with combined systems build storage tunnels and flow controls to reduce overflows. Combined sewers are common in older East Coast and Midwest cities; in California, San Francisco is the only coastal city with one. San Jose’s systems are separate.

Overhead Sewer Systems

An overhead sewer protects a basement from backups when the city sewer overloads. The building sewer leaves the house above the backup level, and below-grade fixtures drain into a sealed ejector basin. An ejector pump lifts the wastewater through a discharge pipe with a check valve into the overhead line. Basements are uncommon in South Bay homes, so overhead sewers are rare here.

Alternative Sewer Systems: Vacuum, Effluent, and Pressure Sewers

Where gravity sewers aren’t practical, because the ground is flat, rocky or wet, or a deep sewer would be too costly, alternative systems are used. Vacuum sewers pull wastewater through sealed pipes with negative pressure. Pressure sewers use a small pump at each property to push wastewater through small pressurized pipes. Effluent sewers let solids settle in a tank at each property and carry only the liquid through smaller pipes.

How Does a Sewer System Work?

A sewer system collects wastewater from properties, carries it through pipes by gravity or pumps, and delivers it to a treatment plant. It works in four stages:

• Collection. When you flush a toilet, run a sink or use an appliance, the wastewater leaves the house through your lateral and enters the public main under the street. Collecting it at the source keeps sewage away from people and the environment.
• Conveyance. Mains join into larger trunk lines and interceptors that carry the flow of whole neighborhoods, growing in diameter as the flows merge. Manholes along the way give crews access to inspect, clean and clear the lines, so sewage keeps moving instead of standing in the pipe.
• Gravity flow and pumping. Most pipes slope steadily downhill so wastewater and solids keep moving. In flat or low-lying areas, or where the flow has to go uphill, gravity isn’t enough: lift stations pump the flow through pressurized force mains to a higher point, and gravity takes over again.
• Transfer to treatment. The flow reaches the treatment plant, where screening, settling tanks, bacteria and disinfection clean it before discharge or reuse. In the South Bay, that’s the Regional Wastewater Facility in north San Jose.

What Happens to Wastewater After It Reaches a Treatment Plant?

The San Jose-Santa Clara Regional Wastewater Facility, one of the largest advanced treatment plants in the western U.S., treats an average of 110 million gallons a day (capacity up to 167) for 1.5 million residents and over 17,000 businesses. It serves San Jose, Santa Clara and Milpitas, plus the Cupertino Sanitary District, the West Valley Sanitation District (Campbell, Los Gatos, Monte Sereno and Saratoga), and two unincorporated districts. Treatment at a plant like this follows six stages:

• Screening and grit removal. Bar screens catch rags, plastics, wipes and other debris, then the flow slows in grit chambers so sand and gravel settle out. This protects the pumps and equipment downstream.
• Primary treatment. In large settling tanks (primary clarifiers), heavier solids sink as primary sludge, and grease and oils float to the top to be skimmed off.
• Secondary treatment. In aeration tanks, bacteria supplied with oxygen consume the dissolved and suspended organic matter. The bacteria clump together and settle out in secondary clarifiers.
• Tertiary treatment. Filtration and further treatment remove fine particles and nutrients such as nitrogen and phosphorus, and disinfection with chlorine or ultraviolet light kills harmful organisms. Advanced plants like San Jose’s treat to this level.
• Discharge or reuse. The treated water, called effluent, is discharged to the Bay or reused. In the South Bay, part of it becomes recycled water for irrigating parks, schools, golf courses, business parks and farmland.
• Sludge treatment. The settled solids are thickened and digested (anaerobic digestion breaks down organic matter and produces biogas), then dewatered. The remaining biosolids are reused or disposed of where regulations allow.

What Is the Difference Between a Public and Private Sewer System?

A public sewer is owned and run by a city, sanitation district or utility and serves many properties. A private sewer is owned and maintained by a property owner, business or private group and serves one property or development. The differences are ownership, who pays for maintenance, and which properties it serves. For a homeowner, the dividing line is usually somewhere along the lateral, and each city draws it differently.

When Is the City Responsible for Sewer Lines?

The city is responsible for the public mains under streets, alleys and easements, and for blockages, breaks and spills in them. In San Jose, the City maintains the sanitary sewer mains, repairs damage and cleans up spills from a blocked main, and responds to sewer spills 24 hours a day. Some City lines run under private property in easements. The City also maintains, as a courtesy, the lower part of a home’s lateral, from an approved property line “wye” cleanout to the main, if one is installed (City sewer FAQ). To report a spill or a main line problem, call the City’s 24/7 line at (408) 794-1900.

When Is a Property Owner Responsible for Sewer Lines?

The property owner is responsible for blockages, damage and maintenance in the private lateral. In San Jose that means the entire lateral, from the house to the main, apart from the City’s courtesy maintenance described above. Other cities draw the line differently. In Redwood City, the owner maintains the upper lateral and the property line cleanout, and the City maintains the lower lateral to the main, but only if there’s a cleanout within 5 feet of the property line. In Mountain View, the owner maintains the lateral all the way to the City main. Check your own city’s rules before work starts; see sewer line vs. water line and insurance for sewer lines.

How Does a Sewer System Compare With a Septic System?

A sewer system is a shared network that carries wastewater from many properties to a central treatment plant. A septic system treats one property’s wastewater on site, in a septic tank and drain field, and the owner maintains all of it. Most South Bay homes are on a public sewer; some rural, hillside and unincorporated properties still use septic. In San Jose, a property that removes its septic tank and connects to the City sewer needs a permit and a property line cleanout (City sewer permit page).

What Are the Key Benefits of a Sewer System?

Sewer systems protect health, keep pollution out of creeks and the Bay, reduce flooding, and make treatment and reuse possible:

• Improve public health. Sewers carry human waste away from homes and public places in closed pipes. The World Health Organization estimates that unsafe sanitation causes 564,000 deaths a year, largely from diarrhoeal disease.
• Prevent disease outbreaks. Untreated sewage can carry the pathogens behind cholera, dysentery, typhoid and hepatitis A. Keeping sewage contained and treated keeps it out of drinking water and food.
• Reduce river and Bay pollution. Untreated sewage adds pathogens, solids, organic matter, nitrogen and phosphorus to waterways, which use up oxygen and feed algae. Treatment removes most of them before the water is released.
• Reduce urban flooding. Storm drains, catch basins and culverts carry rain away from streets and low-lying areas during heavy storms.
• End open disposal of waste. A connected toilet gives waste a contained route to treatment instead of leaving it to contaminate soil and water.
• Cut healthcare costs. Fewer sanitation-related illnesses mean less medical care and less missed work and school. A WHO study in 2012 found that every US$1 invested in sanitation returned about US$5.50 in lower health costs, more productivity and fewer premature deaths.
• Support safe wastewater disposal. Underground pipes keep wastewater contained from the moment it leaves the house until it’s treated.
• Reduce exposure to untreated sewage. Wastewater moves underground rather than collecting near homes, streets and public spaces.
• Support treatment and reuse. Sewers deliver wastewater to plants that can clean and recycle it. Worldwide, WHO reports that 44% of household wastewater was discharged without safe treatment in 2020; in the South Bay, it’s treated and part of it is reused as recycled water.

What Problems Commonly Affect Sewer Systems?

Seven problems account for most sewer trouble, in public mains and private laterals alike:

• Clogs and blockages. Fats, oils and grease (FOG), wipes and debris harden and build up inside pipes until they restrict or block the flow, pushing sewage back up into the lowest drains. Clearing them takes a cable machine or hydro jetting; see signs of a clogged main sewer line.
• Tree root intrusion. Roots enter through cracks and loose joints, grow toward the moisture, catch waste, and eventually widen cracks and break joints. It’s the most common problem in older South Bay clay laterals; see how to get rid of roots.
• Inflow and infiltration (I&I). Rainwater and groundwater get into the sewer through unsealed manholes, improper downspout or drain connections (inflow), and cracked pipes and joints (infiltration). The extra water uses up capacity the sewer needs for wastewater.
• Cracked sewer pipes. Ground movement, settling, heavy loads above and age crack pipes, letting sewage leak out and groundwater in, until a crack grows into a break or collapse.
• Aging infrastructure and leakage. Clay, cast iron and concrete pipe corrode, crack and separate at the joints after decades of service, and need repair, lining or replacement.
• Combined sewer overflows (CSOs). In combined systems, heavy rain can push the flow past capacity and release untreated sewage and stormwater into waterways. San Jose’s separate systems don’t have CSOs, but heavy rain can still overload sanitary sewers through I&I.
• Storm and flood stress. Floodwater can overwhelm sewer lines and pump stations, damage pumps and electrical equipment, and push sewage back up through property drains or out of manholes.

What Are the Best Practices for Sewer System Maintenance?

Twelve practices keep both the public system and your own lateral working. Most are simple habits; the rest are jobs for a professional or the city.

• Control fats, oils and grease. Pour cooled cooking grease into a container for the trash, not the drain. Restaurants use grease traps; homes rely on habits. Recurring slow drains need professional cleaning.
• Keep non-flushables out. Wipes (even “flushable” ones), paper towels and hygiene products belong in the trash. Call a plumber if slow drains or backups keep coming back.
• Plant trees away from sewer lines. Keep trees and large shrubs away from the lateral when you landscape. Roots already in the line need professional removal.
• Check downspouts and sump pumps. Rainwater and groundwater should drain to the yard or storm system, never into the sanitary sewer. Check connections from time to time and have improper ones corrected.
• Know where your cleanout is. Find your cleanout once and keep it clear, so a plumber can reach the lateral quickly in a backup. If it’s buried or missing, a plumber can locate it or add one.
• Monitor sewer odors. Persistent sewage smells point to dry traps, venting problems, bad seals, blockages or a damaged line. Call a plumber if odors persist, keep returning or come with slow drains.
• Plan for emergencies. Know where your cleanout and main water shutoff are, and keep a plumber’s number and the City’s sewer line, (408) 794-1900, handy. In a backup, stop using water and call for help. Our drain and sewer cleaning team answers 24/7.
• Inspect regularly. Watch for slow drains, odors, backups and wet spots, and have an older lateral camera-inspected every few years and before buying or selling a home.
• Clean the line periodically. Where the camera shows roots or grease buildup but the pipe is sound, scheduled cleaning (cabling or hydro jetting) keeps it flowing between inspections; see sewer line maintenance tips.
• Manage root intrusion. At the first signs of roots (slow drains or recurring backups), have the line inspected and the roots removed before they crack the pipe.
• Seal inflow and infiltration sources. Cracked pipe, failed joints and improper connections that let water in should be repaired or lined once an inspection finds them.
• Maintain pumps. Cities and districts maintain their lift stations; a home with a sewage ejector pump should have it serviced and its alarm tested as needed.

What Is a Sewer Scope Inspection?

A sewer scope is a video inspection of the line from your house to the city main. A plumber feeds a waterproof camera on a flexible cable through a cleanout or drain and watches the inside of the pipe on a monitor. It finds cracks, collapses, roots, grease and sags (“bellies”) without digging, which is why it’s worth doing on older homes and before buying one. See sewer scope inspection.

How Much Does a Sewer Inspection Cost?

In San Jose, a sewer camera inspection typically costs $300 to $600. The price depends on the line’s length, how easy the cleanout is to reach, whether the line has to be cleared first, and whether you need locating or a written report. Some companies charge a flat fee and others bill by time; CPI quotes the inspection as a fixed price before it starts. Ask for the video and a written summary with the location and depth of any damage: they’re what you need to compare repair quotes. See sewer inspection cost.

When Do You Need a Professional for a Sewer System Issue?

Call a sewer professional when problems go beyond one slow drain. A camera inspection shows whether the line needs cleaning, a repair or replacement. Call if you notice:

• Recurring sewer backups
• Several slow drains at once
• Persistent sewage odors
• Wastewater surfacing in the yard
• Signs of tree roots in the line
• Cracked, collapsed or damaged sewer pipe
• Clogs that come back after basic drain cleaning
• A need for a camera inspection, repair or sewer line replacement

For a spill or a problem in the street, call the City of San Jose at (408) 794-1900.

The Sewer System in San Jose

• Separate systems. Sanitary sewers go to the treatment plant; storm drains go straight to creeks and the Bay.
• Regional treatment. The San Jose-Santa Clara Regional Wastewater Facility serves San Jose, Santa Clara and neighboring cities.
• Older laterals. Clay laterals under street trees in 1950s to 1970s neighborhoods are where most homeowner sewer problems start.

CPI Service cleans, inspects and repairs sewer laterals throughout San Jose and the South Bay. See drain and sewer cleaning, request a free estimate or call (408) 978-3093.