The intercom blares out, T–– MINUS FIFTEEN MINUTES TO SPLASH. Well, 'smore of an announcer. Never send anything back through it. Mission Control doesn't take notes. Usually. I'm grateful for that. Better when they leave me to my job, and I'm glad they ignore the noise — like that loud banging.

Always ahead of schedule, I'm quick to open the door for my perpetually tardy cohort. An unconvincing bubble pops in my face,

Morning Gray!

Bright eyes in dark circles. She's exhausted. Always late to work. Not sure why. Don't really care. She's good as I am at this, and that's what matters.

Mornin' Oll. Already suited? You're always so eager to see the pump. Just eager to sit down. You're interrupting. If you say so. You didn't have to be the one opening up. Pasc wouldn't. Rather not have mission control complain about delays, either. A minute of their time turns into fifteen of ours. Of mine. Lighten up! Mission Control is really lenient if you ask me! Yeah, else we'd be rid of you a long time ago. Oh I knew you'd miss me, Gray! Didn't say I was grateful for their lenience. Go put your suit on. —And I'm not your mother. Yes, mom!

Suit's tight. Mask's tight. Pack's tight. Thankfully the small-talk was short. It's about a 400 metre swim down to the pump. We swim downstream, pump does most of the work for us. Still be a slog if we had to swim that much everyday. Mercifully, We only need to clean it when problems show up on the pump sensors. Then we lower the pump speed for maintenance. Can't turn this one off, after-all. Not sure it'd ever turn back on. Don't think anyone wants to try. That's why cleaning it is so important.

Pasc's sitting out by the chutes. 3 seats, 3 airlocks. Never grasped why it couldn't be just one. Still, sorta thankful it isn't. I sit down on Pasc's left. She's the best kind of company: keeps her mask tight. Not that we'd have anything to talk about. I'm usually happy to follow her orders.

Oll sits on Pasc's right – means she'll be the first underwater – swimming out front. It's policy to keep the best swimmer downstream of the rest of the team. That's Oll. We depend on her to catch either of us if we get swept down by the current. Mostly me.

The seats lower into the airlocks almost upside down. A breeze blows in for decontamination. The barely notable medical smell seeps through my breather. A vacuum pulls the air right out again, and water rushes to replace it. It's cold. The way it covers my mask is always disorienting. I'll never get used to how the refraction changes and then disappears.

A small indicator on Pasc's mask lights up, and her muffled voice comes through my headset.

…Splash…in…5…

The usual first question people ask about my job is why the pump needs cleaning at all. It's alive, right? Your own heart doesn't need to be cleaned. Least, not usually the kind done by a scrubber in a diving suit. Well, that's wrong. Organs all need to be cleaned. Your blood handles that for you. billions of little cells, all working together to keep it going as long as they can. Long as a few centuries if you're lucky. Antibodies and antibiotics help it go that long.

…4…

Apparently they tried that on the pump a few decades ago. Didn't go as planned. It turns out that introducing antibodies is complicated for the people depending on the water supply, and introducing antibiotics is complicated for the pump. Probably a contributing factor as to why there's only one of these. It works well enough, though. Too well to want to replace it.

…3…

Not that I think we could. Sure, 'smade of live tissue, and 'snot like the little muscle cells are unable to do mitosis, or that they're particularly prone to cancer. In fact, they're suspiciously free of it, for such a large organism. That's the exact problem. We're not real sure of the genetics of this thing. I guess it'd make sense if it came from some kind of animal cardiac tissue at some point, but it doesn't match anything still alive. Nothing anyone knows anything about, at least. As far as geneticists are concerned, it's one-of-a-kind. An endangered species.

…2…

Weird to think of it that way, since. It's. Well. It's a machine, at the end of the day.

…1…

Oll's chute flushes her out, then Pasc's, and mine last. We're in the city's waterworks now. Pasc hails, and we hook ourselves up by the hips. Tethers are more reliable than arms. Least with the right type of karabiner. It's a little scary, honest. The water is still moving as we fiddle with the cord and hook, so you've gotta deal with a little wave going over your whole body, pushing your arms, too. We do a final check on the packed equipment. Mine first, since I carry the most, then Pasc's, and Oll's last.

Three thumbs up. We swim ahead single-file, trying to keep in rhythm with the water going down the pipe. We're half-way to an engraving that says "375m."

I hear they discovered a real long time ago – centuries, probably – that human heart transplants gave the recipient some of the memories of the donor. Just where exactly are those memories? Guess the people at the time must've thought it was part of the soul. How's the soul being transplanted with the tissues, right? It's gotta be in the cells. Some of them, at least.

For that matter, what about animal hearts? I've met people who aren't convinced they've even got souls, so that's gotta complicate things, right? We've been transplanting animal hearts in place of human ones for a few centuries now. Albeit, with immunosuppressors and some genetic modification. Not that I'd want to replace my heart if I could help it, but I wonder if animals have any memories to give to a human donor. Or what it's like to have a soul that's part animal.

Passing 250m. Oll is more serious when she's underwater. Maybe it's the fear. Or a sense of responsibility. She's up front, after-all. I like her better that way. As anti-social as Pasc and I are, none of us want to see each other hurt. Swimming into an active machine is a dangerous job. The valves are powerful enough to serve a majority of the city's water supply. Even at reduced speed, they're strong enough to crush a girl outright. If we had to go through a valve operating at full speed, our jobs wouldn't be possible.

A lot of thought goes into every one of our operations. The equipment, the timing, the decontamination, the insertion point, even the crew. Glad to say there's no one better at this job than us, least for now. 'sNot like we got here by accident……

Why'd you want this job anyway, Gray? It's the heart of the city. Studied it all my life. Well yeah, so did I, but I did it more on a whim. Nobody studies biomechanical maintenance for 6 years 'on a whim,' Oll. I did. Seemed like it would be more fun than failing at being a professional swimmer! Could've chosen any other diving job. And yet, you didn't! So why? …I wonder.

100m. Always shocking how cold the water upstream of the pump is. Seems bizarre that it's so cold, even through a diving suit. It'd feel awful if my insides were ever this cold. Scratch that, if this water was as warm as my insides, I'd probably die. A little warmer wouldn't hurt, though. 'sNot like we've gotta worry about the electricity bill of warming the upstream water a little. Even if it was just for the duration of our missions. We're not allowed to carry any heat sources with us. Safety hazard. For the pump. Screw us, right?

Not that I don't care for the pump's integrity. I do, I really do. Keeps my taps running, a lot better and cheaper than metal pumps do. It's gotta get extra maintenance, but it hasn't needed a replacement in over a century. That's better for us. Least politically. Means the city's got one extra thing it doesn't depend on anyone else for. If anyone ever knew anything about this pump, they've probably forgotten by now, seeing as nobody's heard of another being made. Our university has everything on it, though. It's the only place you can study well enough to do this job.

…Pump…up…ahead… …Gray…move…up…

I give Pasc a thumbs up, and we huddle together. Usually stop halfway to the 25m from the 50m mark near the pump's atrium. Don't want to get sucked into it unprepared while we're detaching the tethers. We enter the ventricle one at a time, and 'snerve-wracking. Real nerve-wracking. Don't think anyone's ever been caught in the main valve, but I'd rather live the rest of my life never having seen it. The tethers might get stuck and pull tight, and then it's caught two people.

I swim toward the valve but Pasc grabs my pack.

…Exterior…

Right. We need to clean the atrium side of the valve first. Almost forgot. Almost. Swimming against gravity, we hug the top of the pipe as it becomes flesh, then tether ourselves to a bar that runs all around inside the atrium. It's positioned just deep enough that you shouldn't get your legs caught in the valve, even if you go limp.

The tools we use are remote, but not radio controlled. Sometimes I wonder why we can't just wire them all the way down, but they'd probably get destroyed faster than we might. Guess the operator training would be even longer, too. Maybe the future will be different.

We stopped checking for cancer a long time ago, so 'smostly surface checks, especially on the valves. They move around enough that it's hard for anything too bad to get on them. Unless they get stuck or clogged, but we'd know about that. Tough mission. Glad it's rare.

Once we've meticulously cleared the surface of the atrium, with relief that nothing showed up on the scan, I mentally prepare myself for passing through the main valve. Oll unhooks from the tether hardpoint, and floats through the entrance as it starts to grow. As she passes to the other side, it closes, slowly. My turn next. It's slow, much slower than a human heartbeat. Three huge wings, growing and shrinking at a rate not much faster than heavy breathing. I think. Mine is too quick to compare against.

My left hand grabs hold of the hardpoint, my right hand grabs my karabiner, and presses it open — the tether retracts, and I stare down the closing valve, left arm shaking. 300kg of red muscle tissue, divided into three flexible wings, each held tight by a ligament piston, powerful papillary cylinders dug deep into the ventricular walls, powerful enough to crush anything close to its size, or smaller. Nothing can get through the valve when it's closed, that's how it pushes almost a hundred million litres of water in less than a minute, every day of every year, long before I was born, and long after I die.

For a moment, as the valve tightens shut, I'm terrified that I won't let go. As long as you start your descent on time, you'll pass through. The huge wings are slowed down for maintenance enough that a metre and a half object should pass through the centre with a tense ease. As the light from Oll's lamp starts to shine behind the shrinking wings, my hands aren't giving way. I try to let go of the hardpoint, the cold and stiff metal bar, but I'm not being dragged with the current rushing past as the valve keeps shrinking away. My arm's all locked up.

Like a mixture of limpness and rushing, the hardpoint suddenly slips away I'm late so I start to swim, as fast as I can I'm late I'm the second one through so that if anything happens, the equipment I'm carrying can be recovered by the last one in I'm late which is Pasc in this case, the team leader I'm late but Oll is there to catch the pack if it makes it through before I do I'm late since the body is too dangerous to recover I'm late and Mission Control insists that you leave it to pass through the pump on its own I'm late it'll end up somewhere down stream and get pulled out that way Oh god I'm late.

I'm sorry to everyone in the city if you end up drinking 0.1% Gray particulate…

The valve has started to close but my body isn't even halfway past it, and I feel my eyes burn. This hasn't happened before, is this how it goes? Who's gonna replace me? 'sNot like we're lining the walls with recruits. I kick as hard as I can, and Oll swims up to me, grabbing me by the neck. The indicator on her mask is flashing. It's been years since I was in university, do they still teach everything we learned? The pump could crush both of us like paper. She should've left me and grabbed the pack. Do people even want this pump? I don't think it's ever killed anyone. Am I going to be the reason it dies?

The water isn't moving. The valve looks tense. Still. Twitching, for a moment, before it closes. Something's tight around me. Oll's still in one piece. I'm still in one piece. It's just us kicking downstream. Inside the ventricle. My face is burning. Her hands feel cold on my cheeks as she looks through my mask. She's crying.

…Lucky…us…?… …Mh…m…!

My chest's squeezed harder. It's warm.

This whole place is warm. Sharp difference from upstream, just across the other side of the valve. The pump keeps the water inside it at a decent temperature. Probably can't help it. It's a muscle, afterall. Exudes heat no matter what. The water cools down after it goes out, though. Nobody ever complains about warm water in their taps, at least.

Pasc drifts in, seeming unshaken. She makes a good leader. Slaps me on the arm, and we begin preparing our equipment again. To keep clear of the pistons, there's no hardpoints to hook in here, so we tether to one another again. As long as we stay upstream of the next valve, it's better than nothing. I'll let you know, 'smuch less stressful on the inside than the outside. This thing isn't shaped like a heart or anything complex, just functionally similar to cardiac tissue.

Honestly, I'm not sure where the shape comes from. It'd be one thing if it was an artificial shape like a pipe, but it's got two halves, an atrium and a ventricle; both longer more than they are squat, and it curls a little. Probably part of its genes, since there's no real external structure to have forced it into any particular shape. It's mostly free-floating in nutrition and oxygen on the other side of these walls. Cleaning over there's a whole other mission.

The surface of the ventricle seems clear as expected, except for a small patch, near one of the papillary cylinders. About half a metre is bulging a little, possibly related to the valve cramping earlier. It shows up fine on the tissue scan, so just a bulge. I press it down gently and it's warm, a lot warmer than my hand. I massage it to keep the tissue even and it… pushes back…? The warmth disappears as the bulge goes back into place.

After the routine scans, we drift down to deal with some trouble. Nothing like surgery, but this is what we came to address: an area about a quarter metre long, and a quarter of that wide. it's stretched by a build-up of some kind. Not sure if it's organic or not, but it shows up nasty in the water purity tests. We'll bring it back with us, and figure out what it is in a lab. First we have to cut it out. Oll grabs hold upstream of it, and Pasc is hanging tethered to her. I'm tethered to Pasc, but swimming a little away from the wall. It's a little exhausting.

I hand Pasc a scalpel, and she starts to scrape at the the build-up. Honestly, this isn't my job. I kind of tune out whenever it comes to operations like this. But Pasc has a fine eye and a finer hand for it. I'm not sure how long passes as she switches between scraping, slicing, prying, and cutting. Gently divorcing the gross build-up from the pump's inner walls. I hand her the tools she wants when she wants them, and go back to sleep.…Lens… Lens. …Vacuum… Vacuum.

Absently staring off. I roll around to look at my cohorts again. What is Oll doing with her hand? She's… petting the wall? I tap her and she glances at me. She seems content to say nothing. I swim up beside her, and place my hand there. It's warm. notably warm. No bulge. I suddenly feel very aware of the fact this thing is moving. It's pumping water, it's beating, like a heart. Odd. I float off again. None of my concern.

Pasc seems about done, with the gunk all secured safe in her pack. That means it's time to go home. We check each others packs, and once everything is secure, we untether, prepared to pass through the last valve. Honestly, after the last one, this one's more of a blur. A rush, since there's no hardpoint to let go of, you just have to go when you go. The valves aren't as muscular, either. We all make it through, and our hips are tied together once more.

On the outside, there's little connective tissue between this outstream valve and the pipe it's connected to. Probably 'cause it's pressed together by gravity and the downstream. Or maybe synthetically. I'm not exactly sure. We haven't been given a reason to deal with that yet. But I'm glad that whatever it is, it means it doesn't have to be cleaned by biomechanics like us.

From here, the airlocks are only 100m downstream. It used to be that you'd swim up from those ones, but after another close call with the valves, it was deemed safer to not fight the current, both for the biomechanics, and the pump.

I feel like I'm dragging my feet, but 'smore like I'm being dragged by the feet. Both by the current, and by Oll. I don't envy her, but I'm glad she's able to do it. We reach the chutes, and for the last time we untether, climbing back up into the airlocks. Grab hold of the handle at the top, and keep your legs clear from the door. No seats here. They're only used for insertion.

The water drains, and the air flows in. it's warm, and blows most of the water off my wetsuit. The door pops open, and I can crawl out. Mission complete. I'm glad we get to sit down for a bit before debriefing, and it's a relief to get this mask off. I take a huge stretch and groan, throwing myself lazily onto the bench, hunched over. Oll sits next to me. Dropping her pack and harness straight from her body, her hands gliding, she gently pushes it aside.

Hey. Oll. Yeah? Why were you rubbing the pump wall back there? …Huh? The ventricle wall. You were petting it. Oh. I guess I was. I dunno. I felt like it. Just like that? Well, it's more like, I was holding onto it for so long that I guess I just felt close to it. Close to it. You felt close to it. Yeah, I felt close to it. Sue me. It's a machine. Nothing more than some muscle cells attached to some pipes and a feeder. You're right, Gray. You're Fucking. Right. Gray. … … You almost died, Gray. I know that, Oll. I Fucking. Know. That. You hold it against the pump? It's a goddamned machine. Hold what against it? I dunno. I don't fucking know. …Gray… Are you tearing up? …I'm glad you're alive, you fuck. Yeah. …Yeah… … 'sNever killed anybody before. I just didn't want to be the reason you all're out of a job. Being out of job would be the least of my— You ever wonder if it's made of human cells? …What? Pasc? Any other animal would be considered a kind of contaminant, wouldn't it? Yeah, I guess so. Not that we'd be able to taste it. …How old are you, Gray? Whoa whoa whoa… She's 27. HEY! Straight from school to school, huh? Guess you've never left this city. …Not really… Trust me, you can taste it. Nothing tastes like our city's water. You're saying it tastes… gross…? No, I'm saying it tastes like the pump. You're insane. Have you been drinking something else? Is that what's going on? Same tap water as you do. Right. Anyhow. We don't know what it is, you studied that much in uni. But it's worth thinking about. Even if it was human at some point, it doesn't match any human DNA we know of. Hell, if it ever was human, that was probably well before it was ever made. I guess so, yeah. That'd be over a century ago, at least. Worth thinking about.

I'm impressed. Pasc's able to undress and dress behind a locker door while spitting out such crap. I'm really impressed. But right now, I could really use a nap. Or some proper sleep. Debrief isn't for another 10 minutes.