Mount Grand

Mount Grand

Where Dunedin's drinking water comes from

I stare entranced at the rows of water tanks. The surface of the water is brown and shiny – bubblebath coated in Gladwrap. This is where our drinking water comes from. Right beneath my feet the alchemical transformation from ‘stream water’ to ‘tap water’ is taking place. Mt Grand Water Treatment Centre, the main source of Dunedin’s water supply. 

The room of flocculation tanks is a big building, a four-car garage at least. Tanks full of water line the room from one end to the other. We are standing on a metal mesh walkway above the tanks. A once-yellow plastic duck catches my eye, bobbing on its side in one of the early tanks. Small monitors, glowing yellow-green, blink numbers at us with mechanical reassurance. The water is murky. The air smells of algae.

Here, the water is getting ‘flocculated’, a process that gets rid of the dissolved organics naturally found in stream water that makes it pale yellow. By mixing in aluminium sulfate (“alum” in water treatment shorthand), the organics un-dissolve and clump together into little particles called flocs. Air bubbles bring the flocs to the surface, where giant scrapers scrape them away.

Flocculation is a complicated process. It’s affected by different pH levels and the water itself is constantly changing. Greg is patiently explaining it to me. Science. pH. Chemicals. I am mostly looking round in fascination, distracted by the strange environment. Halfway down the room, the water in the tanks looks abruptly different: milky-white, not dark. This must be the air, bubbling the floc at the bottom to the top. Yes; I can see the scrapers, they’re pretty intense. Chain links the size of my fist. Is that rust making them red-brown, or dried floc? The scrapers are the length of a table, spaced out at regular intervals across the chain loop like an industrial steampunk Ferris wheel. The scrapers are moving. I hadn’t noticed at first. Agonisingly slow. Like the minute hand of a clock. You really gotta focus. Globs of floc cling to the scraper. Slowly, slowly the scraper slides closer to the edge of the tank. Finally it happens. Sploosh! Floc cascades over the edge, startling in its momentum. Concentrated, it looks less like brown bubbles and more like thin mud, or runny diarrhea. Funny how all waste products look kinda the same. It’s thinning out now, looks more like dirty water. Swish – a giant showerhead turns on, washing the floc out to the sewers. Well, better out than in. I found the process faintly unnerving, things turning off and on without warning. Greg later showed me how everything was controlled by computers – a few letters in the keyboard would shut the whole plant down. 

Our drinking water is collected from Deep Creek and Deep Stream. The water comes through these super long pipes that connect from Central Otago to Dunedin, mostly underground. The pipes weren’t as fat as I was expecting. Maybe 30cm in diameter, which is decent, but this is all of Dunedin we’re keeping hydrated here. 

Mt Grand is ugly-beautiful. Clearly it has been built for utility – no one has bothered to decorate for those nosy Critic writers. The walls of the office building are off-white, black dirt spiderwebbing in the corners. Inside the office it’s a jolting change, austere clean shiny glass, vacuumed carpet, bare walls. I’m in the office for a safety briefing. From the office window I can see a water tank. It’s concrete, light grey gone darker with age, dark rivulets running over the side like tearstained mascara, a cacophony of different aesthetics, beautiful in its dissonance. 

I follow Greg up dizzying flights of mesh metal stairs to check out the first lot of filters. It’s drizzly and it’s cold and I stumble a little because I’m trying to take notes in one hand. “Why are we climbing so high?” I ask. Turns out the pipes are fed by gravity, so the first filters are the highest ones up. Makes sense, now I think about it. Finally we’re at the top. Water gushes out of the pipe, a mini waterfall. I can’t see much else. I ask Graham what these filters mostly catch. Sticks, leaves, dead fish, dead birds. 

Greg takes me down a corridor – floor, walls, ceiling solid concrete. Thin orange pipes wire around the walls. Industrial sci-fi. There are round porthole-esque windows dotted throughout this room. The windows are cloudy with age. Behind them, water. This is the underground view of the water tanks I was viewing earlier. A jet of air bubbles stream out from a nozzle like smoke, wisping and curling and dissipating. These are the air bubbles that turned the water milky white. Greg points out the little floc particles. It looks like dust motes floating. It’s fascinating; through another porthole/window we can see the layer of floc being carried up by the air bubbles. Underneath, the water is empty. 

The treatment plant was a maze of different side doors and tanks and stairs. I stopped trying to learn the geography after a while, content to be led from room to mysterious room, tank to mysterious tank. Our water is dosed with CO2 and lime to balance out the pH, chlorine to kill germs, and fluoride for healthy teeth or whatever. The floors around the lime tanks are splashed white with spilled lime. 

Finally I get to see the finished product. I’m excited. Climb more stairs, through more drizzle. We’re on a rooftop of some sort. Greg lifts the hatch of the tank. I peer in. It looks.... like water. Clear. Smells a bit of chlorine. It’s rather anticlimactic. What was I expecting? I realise it’s - water. I interact with treated town water every day. I brush my teeth, cook my brekkie, flush the loo, and take my showers with this stuff. I know what it looks like. Duh. 

Water is so present in our lives it has become invisible. Take a second to imagine all the water pipes running underneath our streets, in complex networks of pipes and pumps and holding tanks. There are pumps behind bus stops, reservoirs in our parks. Our town council is operating a beautifully complex invisible system of stream-to-tap. And it all keeps flowing. 

This article first appeared in Issue 10, 2017.
Posted 11:58am Sunday 30th April 2017 by Louise Lin.