Sewers.

Millions of people can live right next to one another and regularly poop out tons of potential pathogens.

And thanks to the sewer system, all that bad stuff gets safely whisked away and dealt with.

In places without sewers, those fecal pathogens stick around, making lots of people sick and killing more than half a million people every year.

So we should definitely build sewers in places that don't already have them, right?

Well actually, no.

Hi, I'm David, and this is MinuteEarth.

As great as sewers are, they do have some crappy qualities.

First, because sewer lines are prone to breaking when it gets super cold or super stormy or super busy, in order to be effective, they have to be buried super deep underground, and that makes them super expensive to build and maintain.

Number two, sewer systems work by flushing poops away, but that requires a lot of water, as much as 100 liters per person per day.

And finally, to be useful, sewers must send those poops through a treatment plant that can reliably destroy pathogens.

And there are a lot of places out there where these downsides—costs, water requirements, and pathogen treatment—are total deal-breakers.

Places that don't have the money to install and maintain pricey sewers, dry and drought-prone places without enough water for flushing, and monsoony places where floods can overwhelm treatment plants, sending plumes of poop into local waterways.

Most of the 2.5 billion people that don't already have access to sewers live in places like these, where sewers don't actually make sense.

So is there a better option for dealing with poop in these places?

Well, look at what happened in places without other utilities.

Instead of needing to build big connected power grids and big connected phone grids, we now have the capacities to give people power without power lines, and phone service without phone lines.

Why not sewage service without sewage lines?

There are already a few poop management options that don't require sewer lines, like septic tanks and pit latrines.

But none of these alternatives actually kill the pathogens in poop, which means that if we put them to widespread use, especially in more populated places, they need to be emptied often, exposing people to nasty stuff.

Ideally, we'd have an option that is relatively cheap, doesn't use too much water, and destroys pathogens on site.

And there are some good ideas out there, like this solar toilet that concentrates the sun's rays to burn poops into harmless charcoal.

There's this vacuum toilet that pressure cooks poops into harmless little cakes.

And this steam toilet, which boils poops into harmless piles of sludge.

As an added benefit, once it's processed, the poop can often be used as fertilizer or fuel.

These clever crappers aren't quite ready for primetime yet, but eventually we may be living in a world with fewer sewers to whisk away our poops, and more toilets that can transform them into something turdily awesome.

This video was made in partnership with Bill Gates.

To learn more about how we can improve the lives and health of people around the world, and make safe sanitation accessible to everyone, visit GatesNotes.com.

Thanks Bill!