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I'm about 30km outside Reykjavík, in Iceland.

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And yes, earlier today, I was swimming in
power plant wastewater.

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Which is not something I'd usually recommend.

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If you were at a coal-fired power plant,

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well, even if you were just
swimming in the water

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that had been boiled to spin the turbines
and then cooled back down again,

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well, there are enough stories about
coal ash contamination,

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with arsenic and mercury and selenium,
that it would not be safe.

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For gas and nuclear plants,

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as long as the water's
treated on the way out,

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you'd probably be fine? I think?

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It's one of those things where I wouldn't
want to chance it.

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But that blue-white water is in the Blue Lagoon.

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Now, the management there are very careful
about how they phrase it.

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They prefer to talk about the
skin care and health benefits

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that they claim come from
the silica in the water, but...

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yeah, it's geothermal power plant wastewater.

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Okay, a quick diversion here: most cities
in the world have a cold water mains supply.

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There's a grid of cold water to all
the houses and buildings,

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and it's heated on-demand when it's needed
in each building.

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But Iceland is geologically active:

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in parts of the country, there are
high-pressure reservoirs of hot water

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not too far underground,
where underground rivers meet hot rocks.

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In some places, those reservoirs break through
and reach the surface naturally.

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So near those places, it's economical to drill
a borehole down into the ground

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and capture the superheated, high-pressure
steam and water that come back up.

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There are two things you can do with that
hot water and steam.

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It's not drinkable, first of all,

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it's filled with silica and other bits of
dissolved rock,

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but you can put it in a heat exchanger,

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and use it to heat up fresh, clean cold water,

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and then you can send the resulting
clean hot water

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down a pipeline to paying customers.

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And this is one of those pipelines!

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There is hot water speeding
through this to Reykjavík.

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It doesn't actually feel warm,
if it did the pipe wouldn't be doing its job,

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because the water only loses a couple of degrees
over dozens of kilometres,

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but yes, hot water speeding through that.

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Icelandic cities have separate
hot water and cold water grids.

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If your home is connected to that grid you
don't need a water heater.

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So, okay, that's hot water.
If you want electricity instead,

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you can spin a turbine using the
high-pressure steam that's coming up,

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and generate clean power that way.
Technically, you can do both,

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but pipelines are expensive and there's a
lot of hot water around here,

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so often it's just electricity or hot water.

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Even a massive, industrial-size geothermal
borehole will last a few decades

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before it starts to run out of heat,
and when that happens,

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you can just open another one
a few kilometres away.

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The old one will get back up to temperature
sooner or later,

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the Earth is not going to run out of heat.

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Which means Iceland has a
massive supply of hot water.

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High up on a hill above Reykjavík, there's
this beautiful building called Perlan.

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It's got exhibitions about the
natural wonders of Iceland

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and a revolving restaurant
and an observation deck.

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But the big round things on the outside aren't
part of the exhibitions:

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they're the enormous hot water storage tanks
that the building was built around.

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Perlan is a water tower, just like any other
you'd find around the world,

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except it stores hot water.

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There's so much of it that,
while it's not free, it's very very cheap.

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If your house is a bit too warm in winter
in Iceland, you don't turn the heating down:

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you just open a window and
let some fresh air in.

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Iceland also has quite a lot of fresh air.

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When it's snowing, the pavements are heated
up by hot water pipes underneath.

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Last time I was here was in winter,

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the lake behind City Hall was frozen over,
the ice was strong enough to safely walk on.

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In one corner, there's a pipe constantly pouring
a bit hot water into that lake,

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just so the ducks have somewhere to swim.

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And yes, there are natural hot springs
elsewhere in Iceland,

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there are natural hot spring beaches
elsewhere in the world,

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but Reykjavík has an
artificial hot water beach:

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they just pump hot water into that lagoon
to heat it up a bit.

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There's a hot tub down there!

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But this isn't power plant wastewater.

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It's regular water, like you'd get out of
the cold tap in your home,

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just heated up in a heat exchanger by the
high-pressure undrinkable water and steam

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that comes up from the boreholes
at the geothermal power plants.

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The two never touch.

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So there's one loose end here:

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after that high-pressure steam comes up to
the surface and gets used…

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where does it go?

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Well, once it's cooled down a bit,
the geothermal plants

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just dump the water out onto nearby rocks.

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Those rocks are permeable,
the water slowly sinks through them,

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and over decades it will make its way back
to where it came from.

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Mostly.

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When you're dumping that much water out, though,

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it will tend to form pools and… lagoons.

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Particularly when it's got
a lot of silica in it.

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And the story from there is simple:

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someone went bathing in one of those pools,
thought it helped their skin condition,

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and a few decades of construction
and marketing later

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the Blue Lagoon is one of the
"wonders of the world"

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and they charge more than
€30 for a basic ticket.

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And I don't want to knock that too much!

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Because yes, there is some research that says
bathing in geothermal water like that

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helps some skin conditions,
and there is a big difference

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between wild swimming in a
mysterious hot-water pool

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and bathing in a well-regulated
geothermal spa

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that gives you a towel and
offers in-water massages.

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But if you feel like being cynical, then yes,

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that is power plant wastewater.

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Whew.

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Iceland is beautiful.

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Bit wet. But beautiful.