Used Water Has a Name: Wastewater

Water that has been used—by homes, industries, businesses, or agriculture—and is no longer fit for its original purpose without treatment is universally termed wastewater (or used water, sewage if predominantly domestic).

Composition

• 99.9% Water.
• 0.1% Contaminants: Organic matter (BOD/COD), nutrients (N, P), pathogens, suspended solids, chemicals (pharma, PFAS, heavy metals), microplastics, heat.

Categories

• Domestic Sewage: Toilets, sinks, showers, laundry. Blackwater + greywater.
• Industrial Effluent: Process water, cooling blowdown, cleaning. Highly variable toxicity.
• Stormwater/Urban Runoff: Often combined with sewage (CSOs) or separate (MS4s). Oil, tire dust, trash, bacteria.
• Agricultural Return Flow: Irrigation tailwater, tile drainage. Nitrates, pesticides, salts.

Destination

→ Wastewater Treatment Plant (WWTP) → Primary (settle) → Secondary (biological) → Tertiary (nutrients, disinfection) → Receiving Water (river, lake, ocean) or Reuse (irrigation, industrial, potable reuse).

Terminology shift: "Wastewater" → "Used Water" → "Resource Water" reflects circular economy thinking. It's not waste; it's water in the wrong place with the wrong chemistry.