Brief description

A network of underground pipes and facilities dedicated to collecting and transporting wastewater and refuse from buildings to a treatment or disposal site.

Use / Function

• Primary use: Hygienic removal of human waste (sanitation) to prevent disease.
• Secondary uses: Drainage of stormwater to prevent flooding.
• Scale: Urban and industrial.

Operating principle

• Gravity Flow: Sewers are laid on a precise downward slope so liquids flow naturally without pumping.
• Traps: U-shaped bends in pipes at inlets (sinks, toilets) hold a small amount of water to block sewer gases from entering buildings.
• Venting: Vertical pipes allow air to enter the system, preventing vacuums that would suck traps dry and ensuring smooth flow.

How to create it

1. Surveying: Determine the natural slope of the terrain towards a low point (river, treatment plant).
2. Trenching: Dig trenches deep enough to ensure a constant gradient (usually 1-2%).
3. Laying Pipes: Install large diameter pipes. Ensure joints are watertight to prevent groundwater contamination.
4. Manholes: Install access points at regular intervals and every change of direction for cleaning and inspection.
5. Connections: Connect building drains to the main sewer line.

Materials needed

• Pipes: Ceramic (glazed clay), Concrete, Plastic (PVC), or Brick (historical).
• Structure: Brick and Mortar for manholes.
• Tools: Shovels, Levels, Pickaxes.

Variants and improvements

• Combined Sewer: Carries both sewage and stormwater. Cheaper to build but prone to overflowing raw sewage during heavy rains.
• Separate Sewer: Distinct systems for sanitary sewage and stormwater. More expensive but environmentally safer.
• Septic System: A local, on-site version for isolated buildings using a tank and leaching field.

Limits and risks

• Blockages: Accumulation of grease, roots, or solid objects can cause backups.
• Overflow: Heavy rains can overwhelm combined systems.
• Health Hazard: Direct contact with sewage causes cholera, dysentery, and other diseases.
• Gases: Methane and hydrogen sulfide build up in sewers; they are toxic and explosive.

Related inventions

• Latrine: Basic disposal.
• Toilet: The primary source of waste.
• Septic Tank: Local variant.
• Drainage: Managing surface water.
• Water Supply: The input counterpart.
• Hand Washing Basin: Source of greywater.
• Pipes: Core component.