(contemplative piano music)

[Narrator] Tap water.

To the average American, it's as dull as, well, dish water

But even though you can't see it, there's a lot going on

when we dive deeper to see what's inside.

Like sulfates, which determine hardness,

and no, we're not talking ice cubes.

In this case, hardness refers to water

with a high mineral content,

like the stuff you might drink at a spa,

though it can be hard on plumbing,

leading to the formation of limescale

and the heartbreak of soap scum.

That's why water is typically softened

with ion exchange resins and polymers.

Or you can just wait for nature's own hydraulic cycle

to soften and purify H20 the old-fashioned way,

through evaporation, condensation,

and eventually, precipitation.

Hard or soft, though, tap water is typically

an invisible cocktail of whatever impurities

it's picked up along the way to your faucet.

For example, the Big Apple boasts about the quality

of its drinking water from upstate reservoirs,

but not so much about the potentially unhealthy

levels of lead that can leach into the liquid

as it travels through the pipes of the city's

ancient plumbing system.

And purification agents are often as bad

as the impurities that they treat, like chloramines,

which can damage red blood cells in high doses,

or trihalomethanes, which are meant to kill microorganisms,

but may damage your liver and DNA.

Don't worry, though.

Assuming there's no fracking nearby,

your tap water's probably safe and non-flammable,

especially if you catch the impurities in the pores

of the activated carbon or ion exchange resin

inside most commercial point of use filters.

And since healthy hydration is the key to long life,

we'll definitely drink to that.

(ethereal laser tone)

Enjoy other episodes of What's Inside

by subscribing to the Wired channel.