Toilets

or: a city-sized chemistry plant for your poop

Your city pumps in river or well water and runs it through an actual chemistry plant, where chemicals clump the dirt into blobs that sink, the water trickles through sand, gravel and charcoal, and chlorine kills whatever made it through, all to meet federal limits on more than 90 contaminants¹. Then miles of pipe deliver that drinking-quality water to your house, where the toilet uses nearly 30 percent of everything that comes in², at up to 1.6 gallons a flush, because Congress passed a law about it in 1992³.

And we poop in it.

How it works, badly

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Chemicals clump the dirt into blobs that sink.
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Sand, gravel and charcoal filter it, and chlorine finishes the job.
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Clean drinking water travels to your house.
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And we poop in it.

Wait, is that real?

Yes, the water in your toilet passed the same tests as the water in your glass.

The chemistry plant↩

Community water systems that draw from rivers and lakes typically treat water in four steps, according to the CDC. Coagulation and flocculation add positively charged chemicals that bind dirt and dissolved particles into clumps called floc. In sedimentation, the floc sinks. Filtration runs the clear water through sand, gravel and charcoal to remove particles, parasites, bacteria, viruses and chemicals. Disinfection with chlorine or chloramine kills what’s left. The EPA regulates 90+ contaminants in drinking water.

The biggest indoor user↩

The EPA says toilets account for nearly 30 percent of an average home’s indoor water use. Older, inefficient toilets can use as much as 6 gallons per flush, and replacing them with WaterSense-labeled models can save nearly 13,000 gallons per home each year.

The law about flushing↩

The Energy Policy Act of 1992 requires new toilets in the U.S. to use no more than 1.6 gallons per flush. The EPA’s voluntary WaterSense label goes further, to 1.28 gallons or less, at least 20% below the federal limit.

The fine print↩

Well water from underground often needs less treatment than river water, and steps vary from city to city, so "an actual chemistry plant" is truest for systems that draw from rivers and lakes. The 30 percent is an average across homes. Toilets installed before the law can still use more than 1.6 gallons. "Miles of pipe" depends on where you live.

Sources: CDC: water treatment (archived); EPA WaterSense: residential toilets; Wikipedia: EPA WaterSense

Last fact-checked October 29, 2026.