Around the US drinking water comes from  rivers, reservoirs, underground aquifers   and the toilet.

Yeah, we've gotten so good at  cleaning water that in some places you can take   the dirtiest water you can possibly think of and  make it a refreshing drink again.

So how?

Le ding.

If I can summarize a really bad situation here,  in a lot of places we're running out of clean,   accessible water for people who need it.

Some  reports predict that in the next 50 years,   the US fresh water supply could be reduced by  a third, and there's not just a lot of places   to go out and get it from.

Out of all of the water  on earth, only a little bit of it is fresh water,   just 3%, and most of that is inaccessible.

Either frozen in polar ice caps or way   underground.

So when we drink water or  shower in it and then just flush it away,   in a lot of places we are throwing away perfectly  good water that we need if only we could clean it.

In fact, only seven to 8% of  waste water in the United States   is reused.

So now some places have started  to super clean the water that we flush down   the drain so that it can be reused, not  just for stuff like watering plants,   but also for drinking.

Typically, we clean  water that we intend to drink called potable   water for two reasons.

To make it taste good  and to take out stuff that could make us sick,   and there's lots of stuff you want to take  out of water before you drink it.

Bacteria,   heavy metals, chemicals, viruses, even just plain  old dirt.

Drinking contaminated water can make   you really sick.

Things like typhoid, cholera  and polio are all transmitted by dirty water.

Here in the United States, the EPA actually  regulates 90 different contaminants in drinking   water, setting safe standards for each one.

Things like cryptosporidium, legionella, bromate   and that's not all of them.

Now for a long time  in human history, before we knew that bacteria   in our water could make us sick, we just cleaned  water to make it taste better before we drank it.

So as far back as 2000 to 1500 BCE, Indian and  Greek writers talked about straining water to   get the dirt out.

Sanskrit and Greek writings  of a similar time both mention heating water   either by boiling it or setting it out in the  hot sun or inserting a hot metal rod in it.

You can also coagulate all the junk  in water together to make it drop out,   and people have been doing this as far  back as ancient Egypt using alum.

Alum   or aluminum sulfate coagulates stuff together  because it forms positively charged ions in water.

Negatively charged dirt molecules  would typically repel each other   but when alum is present, the dirt grabs onto  the positive ions, neutralizing their charges   and allowing them to clump and fall  down to the bottom of a tank of water.

In the 1700s, scientists started to explore the  adsorbing powers of activated carbon and that   is adsorbing not absorbing.

Activated carbon  or charcoal is the same stuff you find in your   standard fridge water filter or a fish aquarium  filter.

It's typically made by burning something   carbon rich like wood at really high temperatures  and then exposing it to some sort of chemical   treatment or to oxygen to make it more porous.

Those pores give it a really high surface area,   usually between 300 and 2,000 meters squared  per gram.

That's 10 tennis quarts of area   inside a single gram of charcoal.

That huge  surface area means lots of binding sites for   impurities that get stuck in the pores.

Things  like volatile organic compounds and chlorine,   which can just make your water taste bad or things  like diesel fuel and medications that can make   you sick.

It doesn't necessarily have to be as  scientifically packaged as a fridge water filter.

Stuff like this, which is literally just a  chunk of charcoal in a pitcher will also work.

It really can pull out stuff that can make  your water taste kind of stale or chloriney.

Straining coagulation and carbon filtering  can all make water both taste and look better,   but they can still leave behind bacteria  and viruses that can make you sick.

It wasn't until the late 1800s during  an outbreak of typhoid in Maidstone,   Kent, when people first started exploring  the idea of adding a little bit of bleach   into the water supply to try and sterilize it.

A cutting edge paper of the time from 1894 had   suggested that adding bleach to water could make  it germ free and it was right.

Typhoid deaths   dropped dramatically and adding chlorine bleach  to water started to save lives across the world.

When bleach, typically sodium hypochlorite,  dissolves in water you get hypochlorous acid.

This   acid disrupts the lipid membranes in bacteria and  some viruses.

Sodium chlorite in water can also   produce hydrogen atoms and hypochlorite, which can  denature proteins throughout the cell.

Like all   of the other contaminants that the EPA monitors,  there's a top limit to how much lingering chlorine   from the broken down bleach you can leave in the  water, usually around four milligrams per liter.

Too little to hurt us, but enough to punch  some holes right through bacterial membranes.

Now all of that is stuff that we do to clean  water before it comes into our homes.

But when   we want to clean the water that leaves our homes,  we can do some similar processes by sending it to   wastewater treatment plants.

Today in the United  States, there are more than 16,000 wastewater   plants in the country.

Most have two stages of  cleaning, primary and secondary.

First, water goes   through preliminary treatment, which screens out  things like branches and plastic bottles.

And then   it goes to primary settling chambers where heavy  objects like gravel and biosolids, and yes, that's   poop, can settle out.

Wastewater treatment plants  often also add benign chemicals like organic   polymers or ferric chloride to the water to  help coagulation and settling during this stage.

Secondary cleaning takes care of small organic  matter in the wastewater using bacteria.

Think   dissolved fats, and lipids and sugars that  come from your kitchen or your bathroom.

The wastewater plant mixes bacteria and  air into the water and the bacteria eat   up all of that organic junk.

This is just  like what would happen to water in a lake,   pond or other wetland.

Wastewater plants just help  speed up the process in a controlled environment.

If headed back to fresh water, the remaining  liquid is usually disinfected with something like   chlorine to get rid of any remaining bacteria  that escaped the secondary treatment step.

This system makes water that's pretty clean and  safe to return to the environment, but if we want   to make it clean enough to drink, there's some  other things that we need to filter out first.

Things like medications and microplastics,  and there's some other new innovations that   can help to make the water that we filter taste  better and be better for the environment too.

First, while chlorine can be super  safe and effective for cleaning water,   water treatment plants usually have to remove any  excess chlorine before that water can be released   back out into the environment.

This is because  chlorine and its products are toxic to lots of   aquatic and marine organisms.

So some places  are turning to peracetic acid.

Peracetic acid   has the same bacteria punching abilities of  chlorine, but when it breaks down in water,   it turns into just acetic acid, or vinegar,  and hydrogen peroxide, which can break down   further in water to be just water and oxygen.

You can release the resulting clean water into   a stream or waterway without having to worry  about deactivating any excess chlorine first.

Second, our water also contains a contaminant  we haven't talked about at all yet,   microplastics.

When plastic breaks  down tiny pieces of it wind up   literally everywhere in our environment,  including our wastewater and our waterways,   and according to a couple of recent new  studies also in our blood and lungs.

Awesome.

Microplastics can be hard to remove  from wastewater because they're so small.

Some   wastewater plants do have filters designed to trap  them, and don't just imagine these as screens.

Some of them also look like these adorable  fuzzy balls.

Other microplastics get pulled   down by normal coagulation processes like the alum  that we talked about before.

But some of the most   common coagulants, things like polyacrylamide,  which can create a sticky gel, can break down   into potentially harmful byproducts that are  hard to remove and filter out from the water.

So scientists have been looking for alternatives.

One really cool recent paper suggests a delicious   one, okra.

Yes, like the food.

You know how when  you cook okra it can get a little bit slimy?

That slime is called mucilage and scientists  wondered if this sticky sugar rich substance   would help to trap water contaminants, and it  turns out that it can.

The idea is that all of the   slime grabs onto the microplastics and pulls them  out of the water without leaving those potentially   harmful molecules behind.

The study found that  okra plus fenugreek extracts worked really well   to remove microplastics from ocean water, while  okra and tamarind pulled microplastics out of   fresh water best.

Since all of the coagulating  sugars themselves are food grade materials, any   leftovers in the water supply will still be safe  to drink or to flush out to the ocean.

Delicious.

Water that comes out of our homes can  also include things like medications,   either from people flushing or peeing drugs  down the toilet.

People also tend to pour   unused household chemicals like pesticides down  the drain too.

So if you want to drink that water,   you've got to get all of that stuff out of  it.

Some water treatment plants have turned   to micro-filtration followed by reverse  osmosis to get those things out.

Yes,   that is the same process described on the side  of your overpriced water bottle.

Reverse osmosis   works by using pressure to push water through a  membrane that only allows water molecules through,   leaving dissolved molecules, including  those things like drugs and hormones behind.

A study on Los Angeles water treatment plants  found that those that used reverse osmosis to   help clean water removed two to three times more  medication from the water supply than those that   didn't.

By adding together combinations of  these water technologies, water treatment   plants in areas where water is scarce, say like  the deserts of the American Southwest, are able   to confidently clean household wastewater.

And yes, I mean water from your toilet,   and then put it back into the drinking water  supply.

Considering that Southern California   alone sends as much as 830 million gallons of  treated water per day just out into the ocean   rather than back into a place where we can use  it, that is a lot of valuable water that we're   not taking advantage of.

Especially as we  find ourselves in worse and worse droughts.

Though some people find the idea of  drinking cleaned wastewater a little weird,   but honestly, I thought for a really long time  that's just what we did with wastewater.

Why would   we clean water and then just dump it back into the  river?

I thought we drank it.

In Orange County,   California cleaned wastewater undergoes not  just micro-filtration and reverse osmosis,   but UV disinfection as well before going back  into the drinking supply.

It filters into   the environment around the San Gabriel River  before making it back into deeper groundwater   that's then added to the drinking supply.

This process is called indirect potable reuse.

El Paso, Texas in the middle of the  desert with disappearing water sources,   also reuses wastewater as direct potable reuse,  which means that you can drink it right away   after it's cleaned, rather than waiting for  it to filter through the environment first.

It just makes sense to do this when you need  water in the middle of the desert and more and   more water strapped locations are looking to  make the switch soon.

The barrier now isn't so   much scientific as it is psychological.

We can  make the water safe and clean, but some people   still feel turned off by the idea of drinking  toilet water.

Really, we just need a good rebrand.

Look, there are a lot of ideas out there for  how to get over this from name changes for water   programs to terrifying mascots like Singapore's  Water Wally and Phoenix's Wayne Drop and Lou Poo.

Yes, these are real, but in the end, it's  all chemistry.

Once you've cleaned it,   the water is the same H20 no matter if it  comes from a lake or your own bathroom.