How Your Bathroom Works: A Plumbing Primer


Modern plumbing is a wonderful luxury we should sincerely appreciate every time we turn on a tap.  500 years ago kings and queens couldn’t get a hot bath without flunkies to carry around tubs full of water.  In 1950, a quarter of US households didn’t have flush toilets in their homes.  

How often do you think about how modern plumbing works? 

All modern plumbing works using few basic principles:

Don’t Cross the Streams

Clean water in, dirty water out and never the twain shall mix.  Every building with plumbing has two separate water systems, one that brings in clean potable water (likely from the municipal supply), and a separate one that gathers water from all the drains and takes it back out of the building. The two systems interface at each fixture – a device that lets clean water in and dumps out waste.

(Smelly) Gas won’t pass through liquids

If every fixture is connected to the city sewer system by an open pipe, why don’t all out bathrooms smell like … sewage … all day every day?  Every fixture has a U shaped section of pipe – a trap –  that holds standing water all the time.  Gas (sewer smells) don’t go through that pool of water and your bathroom smells fresh and clean.

Note: sometimes when a sewer smell starts coming up from your basement it may be because the trap water in a rarely used floor drain has evaporated, opening a gap for gas to pass through.  Pouring a little water down the drain will fix that problem.

Gravity –  it’s not just a good idea; it’s the law

Fresh water comes into your house and the dirty water leaves it by the power of simple gravity.  Municipal water towers are higher than all the fixtures they supply.  Likewise, when you flush your toilet, water stored high (in the toilet tank) is allowed to flow down, and the rush of its passage sweeps itself and anything else through the trap and on down out of the house.

In some cases plumbing fixtures in a basement will be lower than the city sewer lines and need to be pumped up with a sewage ejector pump, in order to be able to flow back down again.  Its a perfectly viable system but gravity works better – there’s literally never been an outage in gravity.

Next time you take a bathroom break, take a moment to contemplate how much our lives are improved by good plumbing … and how much more we can improve modern bathroom design with a few easy changes in thinking (hint: details to follow on Thursday).