Why did a Canadian town’s water supply turn pink?

Pink water. Image: Magic Momentz/Flickr/creative commons.

Most of us take it for granted that the taps in our homes will deliver safe and clean water for drinking, cooking, showering and cleaning. This means there is usually little interest from the public in how the water gets there. However, it took less than a day for a story from Onoway, a small town in Alberta, Canada, with just over 1,000 residents, to make it from social media to global newsfeeds. “Bright pink water comes out of taps in Canada!” – suddenly we are all interested in water treatment methods. The Conversation

To enjoy the benefits of clear and safe water, a hidden but valuable infrastructure of water treatment exists in our cities and villages. These are operated and maintained by engineers and scientists, and among them are water chemists. These chemists have been investigating the use of neat chemical reactions to remove undesired chemicals and potential pathogens from naturally sourced water and to prepare the water for its safe journey through distribution systems.

The local drinking water treatment plant of Onoway treats its water using potassium permanganate. This is an almost black looking solid which forms a bright purple solution in water and also removes dissolved iron and another metal called manganese.

Iron and manganese are not harmful to human health, but if these metals are present at high concentrations it can lead to deposits in the water distribution system and discolouration of the water. However, the auburn tints of iron seem boring compared to the spectacular pink that has raised global interest and lively social media discussions.

Customers are very sensitive to the colour, taste and odour of drinking water – these are the human senses used to assess water quality – so this incident has understandably caused alarm. The pink colour stems from some potassium permanganate that escaped through a failed valve and into the drinking water distribution system, eventually ending up with the customers.

Potassium permanganate has been used in drinking water treatment for more than 100 years. In addition to iron and manganese removal, it is used to remove taste and odour as well as to control undesired algal or mussel growth in treatment works. It also has disinfecting properties. Permanganate forms solid, black manganese dioxide when it reacts with the water contaminants – and this can then be filtered out of the water.


A little goes a long way

Potassium permanganate has the chemical structure KMnO4 and is a compound that is electron deficient – that is, it doesn’t have enough electrons. This lack of electrons makes it a strong oxidant that readily reacts with a wide range of unwanted compounds in water. It belongs to an established group of water treatment chemicals that can be summarised under the term “conventional chemical oxidants”, which also include oxygen, chlorine, chlorine dioxide, ozone, hydrogen peroxide and, in the wider sense, UV light.

Water is typically treated with a dose of 1-3mg of potassium permanganate per litre of water, which is quite a small amount. But only unreacted potassium permanganate has a visible pink colour in water and is visible even at very low concentrations – as low as 0.05 mg per litre of water – so it doesn’t take much to add colour.

Since only small quantities of permanganate can change the colour of water, customer complaints relating to residual permanganate are known to occur . This means treatment works usually take care to remove any unreacted, coloured permanganate before the water reaches consumers.

The pink water does not pose a threat to human health but skin irritation related to potassium permanganate is known at a certain concentration. Onoway’s mayor claimed that customers were not at risk. However, these concentrations seemed to vary – some had water merely tinted pink whereas some water was bright purple. Regardless of what shade of pink they receive, customers are advised to rely on alternative drinking water sources until the permanganate is flushed out of the distribution system.

Water treatment isn’t simple

For water treatment, there is no one-size fits all approach. Drinking water treatment processes vary due to different local water resources and what the traditional and established technologies are. Iron and manganese can be removed by alternative methods, such as aeration, which uses the oxygen present in the air, or by running the water over catalytic granules consisting of manganese dioxide. But every method has its specific advantages and disadvantages.

Many parameters need to be evaluated before making an informed decision on which method to use to treat a water supply – but there’s no doubt that potassium permanganate is one of the more colourful methods.

Jannis Wenk is a lecturer in water science and engineering at the University of Bath.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

The Delhi Metro: How do you build a transport system for 26m people?

Indraprastha station in 2006. Image: Getty.

“Thou hath not played rugby until thou hath tried to get onto a Delhi Metro in rush hour,” a wise Yogi once said.

If you’ve never been on New Delhi’s Metro, your mind might conjure up the the conventional image of Indian trains: tawdry carriages, buckets of sweat, people hanging out of windows and the odd holy cow wandering around for good measure.

Well, no. The Delhi Metro is actually one of the most marvellously sophisticated, affordable, timely, and practical public transportation systems out there. On a 45C day in the Indian summer, many a traveller has shed tears of joy on entering the spacious, air-conditioned carriages.

Above ground, Delhi is a sprawling metropolis of the scariest kind: 26m people, three times the population of London, churn and grind through Delhi itself.

The National Capital Region, an area which includes Delhi and its surrounding satellite cities – now victim of its never-ending urban sprawl – has an estimated population of almost 50m. So how do you tie such a huge population together?

The map; click to expand. Image: Delhi Metro Rail.

Motorised vehicles won’t do it alone. For one, air pollution is a horrific problem in Delhi, as it is across India. Last November, the government declared a state of emergency when the Indian capital was engulfed by a toxic, choking fog so thick that you could barely see several metres in front of you, drawing allusions to the great Victorian fogs in London.

Then there’s Delhi’s famous traffic. Twenty-five years ago, the travel writer William Dalrymple observed that you could reduce the Delhi’s road laws to one simple idea: the largest vehicle always had the right of way. The traffic has tamed somewhat in the 21st century, but the number of vehicles has multiplied again and again, and it’s not uncommon for people to be stuck in four-hour traffic jams when they try to traverse the mighty city.

Enter the Delhi Metro – a huge network of 164 over- and underground stations – and by any account, a titan of civil engineering and administration.

The numbers are simply colossal. Every day the metro serves on average almost 3m people. Annually, it carries around 1bn.

In a country where intercity trains still turn up a day late, the Delhi Metro is extraordinarily timely. On the major lines, trains will come every several minutes. The trains are extraordinary speedy, and you’ll reach your destination in a fraction of the time it would take for you to drive the distance.

The minimum fare is 10 rupees (12p); the maximum fare, to and from the airport, is 50 (60p).

The evolution of the metro. Image: Terramorphus/Wikimedia Commons.

Construction of the metro system began in 1998, with the first section completed in late 2002. Keen to avoid the catastrophic corruption and bureaucratic mismanagement which plagued eastern city of the Kolkata Metro, developers took advice from Hong Kong’s high-tech system There have been several stages of development to add extra lines; more is planned. By 2020, it is hoped that the 135 miles of line will have increased to over 300.  

One thing quite striking about the metro is its women’s only carriages at the rear and the front of the train, marked by pink signs. Sexual assault and harassment has been a horrific problem on Delhi’s transport systems. Women can of course go anywhere on the train – but men who violate the carriage system will have to deal with the scathing anger of the entire pink carriage.


One of the under-discussed impacts of widespread and well-used public transportation systems is their propensity to break down social and class barriers over time. As the London Tube began to be used more and more in early 20th century London, people from completely different walks of life and classes began to brush shoulders and share the same air.

The story is similar in Delhi. The necessity of the metro helps to break down old caste and class divisions. Of course, many elite Delhiites would not be seen dead on the metro, and choose their private chauffeur over brushing shoulders with the common man. But slowly and surely, the times are a changing.

What’s more, the Delhi Metro system is one of the greenest around. Six years ago, the Metro was the first railway system in the world to be awarded carbon credits from the United Nations for helping to reduce pollution in the capital by an estimated 640,000 tonnes every year.  

All praises sung and said, however, at peak times it’s less mind the gap and more mind your ribs – as a fifth of humanity seems to try to get on and off the train at once.

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