How Cities Get Their Drinking Water

Fresh drinking water has to go through quite the process before it’s safe enough for us to drink. Here’s how our water goes from river to refrigerator, from aquifer to Aquafina and from stream to SodaStream (can’t stop, won’t stop). 

How cities get their drinking water

The source

There are two kinds of water sources: groundwater and surface water. They’re both fairly self-explanatory, but they both collect water from snow and rain in some form or another.

If you remember the water cycle lesson from middle school (or was it elementary school?), then you can probably picture at least one version of a water cycle infographic. Rain or snow falls from the sky and, either over a few days or over hundreds of years, makes its way to a lake, a stream, a river or, in the case of groundwater, an aquifer. 

These freshwater sources are where we start the process of collecting our drinking water. Around 64% of public water systems are supplied by surface water, and about 36% is supplied by groundwater.

Catchment

Finding fresh water is one thing, but getting it to a treatment center is another thing entirely. 

Groundwater is accessed either at a naturally occurring spring or via a well, after which pumps and pipes transport the water to the treatment center. Freshwater can be collected from the surface with a series of pipes. 

A simpler version of a catchment system is a rain gutter! In many cases, people collect rainwater by piping a gutter straight into a storage container. This can be an eco-friendly solution in places that have limited surface and groundwater sources. 

Screening

If you’ve ever gone hiking and had to drink from a freshwater source, you’ve probably tasted some grit and grime that occurs naturally as water pumps through the ground. Not all freshwater is perfectly clear or clean, so before the water arrives at a treatment plant, it’s time to filter out all the unwanted material. 

The first step in this treatment process is to sift out all the big debris, which is usually done at or close to the source. This screening process uses a large metal screen to stop large objects like leaves, twigs, fish, trash and other chunky items from entering the pipes. 

Coagulation & flocculation

The drinking water has arrived at the treatment plant without any of the large debris, but there’s still plenty of microscopic dirt and debris saturating the water. This debris is too small to filter through a screen, so positively charged chemicals are added to the water to bind with the negatively charged particles of dirt. This coagulation creates a thicker substance called floc.

Sedimentation

Now that the floc is thicker and heavier, it’s easier to filter it out of the water.

The water is pumped into large vats where it is allowed to rest, allowing the floc to sink to the bottom and settle. Once the floc is all settled, it’s easier to remove the sediments from the now-clarified liquid.

Ozonation

Once sediments have been filtered out of the water, the water goes into yet another step to filter out any microbes and bacteria left in the water. It’s usually at this point that water treatment processes begin to differ depending on the city, state or region. 

Some treatment processes include ozonation, which involves adding ozone gas to the water. 

Ozone molecules can kill any microbes in the water, as well as break down pesticides, minerals and other chemicals floating through the water. This leaves the water smelling and tasting better.

Filtration

Although most of the particles and chemicals have been broken down, there’s still a lot of gunk in the water that needs to be removed. 

A series of filters made from sand, gravel and charcoal trap the remaining particles and allow the clear water to filter down to the next stage. 

Disinfection

Now that the water is finally free of particles and microbes, it’s almost ready to be distributed to the public. Here’s where treatment centers can add the additives and chemicals they want to disinfect and treat the water for the region.

Most centers will add chlorine gas or chloramine, which is safe for humans and pets, to kill any remaining parasites, germs and viruses. This is where germs like salmonella are killed, so it’s a vital step in keeping us healthy and disease-free.

This is also where centers can add fluoride, if that’s what the cities choose to do, which is good for tooth and oral health. 

Storage

The water is finally fully treated and ready for use, so It’s pumped to water towers or reservoirs for storage. Gravity and pressure pump the water into your home’s pipes so that when you open a faucet or flush a toilet, you have fresh, clean water immediately accessible. 

What does your city use?

If you’re interested in seeing what your city, county or region uses for a water source, you can explore this interactive municipal drinking water map made by the Environmental Protection Agency. 

You can also contact your city’s public works department to find out whether they add fluoride to your water, or whether their water treatment plant uses biological or chemical treatment processes.

If nothing else, hopefully this helps connect the dots between the water you’re pouring into your tea and the place from which it comes. It’s a long process to treat water well enough to drink, so let’s do our part in preserving our resources and using water wisely!

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Featured photo courtesy Pixabay/Baudolino