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.

 
 
 
 

Never mind Brexit: TfL just released new tube map showing an interchange at Camden Town!!!

Mmmmm tube-y goodness. Image: TfL.

Crossrail has just been given a £1bn bail out. This, according to the Financial TImes’s Jim Pickard, is on top of the £600m bailout in July and £300m loan in October.

That, even with the pound crashing as it is right now, is quite a lot of money. It’s bad, especially at a time when there is still seemingly not a penny available to make sure trains can actually run in the north.

But the world is quite depressing enough today, so let’s focus on something happier. On Saturday night – obviously peak time for cartographic news – Transport for London emailed me to let me know it would be updating the tube map, to show more street-level interchanges:

Connections between several pairs of stations that are near to each other, but have traditionally not been shown as interchanges, now appear on the map for the first time. These include:

  • Camden Road and Camden Town
  • Euston and Euston Square
  • Finchley Road and Finchley Road & Frognal
  • Kenton and Northwick Park
  • New Cross and New Cross Gate
  • Seven Sisters and South Tottenham
  • Swiss Cottage and South Hampstead

The stations shown meet a set of criteria that has been used to help determine which should be included. This criteria includes stations less than a 700m or a 10 minute walk apart, where there is an easy, well-lit, signposted walking route and where making the change opens up additional travel options.

The results are, well, this:

In addition, interchanges between stations have traditionally appeared on the Tube map as two solid lines, irrespective of whether they are internal or external (which means customers need to leave the station and then re-enter for the station or stop they need). This approach has now been updated and shows a clear distinction between the two types, with external interchanges now being depicted by a dashed line, linking the two stations or stops.

And lo, it came to pass:

I have slightly mixed feelings about this, in all honesty. On the positive side: I think generally showing useful street-level interchanges as A Good Thing. I’ve thought for years that Camden Road/Camden Town in particular was one worth highlighting, as it opens up a huge number of north-east travel options (Finchley to Hackney, say), and apps like CityMapper tell you to use it already.


And yet, now they’ve actually done it, I’m suddenly not sure. That interchange is pretty useful if you’re an able bodied person who doesn’t mind navigating crowds or crossing roads – but the map gives you no indication that it’s a harder interchange than, say, Wanstead Park to Forest Gate.

The new map also doesn’t tell you how far you’re going to be walking at street level. I can see the argument that a 400m walk shouldn’t disqualify something as an interchange – you can end up walking that far inside certain stations (Green Park, Bank/Monument), and the map shows them as interchanges. But the new version makes no effort to distinguish between 100m walks (West Hampstead) and 700m ones (Northwick Park-Kenton), which it probably should.

I’m also slightly baffled by some of the specific choices. Is Finchley Road-Finchley Road & Frognal really a useful interchange, when there’s an easier and more direct version, one stop up the line? No hang on West Hampstead isn’t on the Metropolitan line isn’t it? So that’s what it’s about.

Okay, a better one: if you’re switching from District to Central lines in the City, you’re generally better off alighting at Cannon Street, rather than Monument, for Bank – honestly, it’s a 90 second walk to the new entrance on Walbrook. Yet that one isn’t there. What gives?

The complete new tube map. The full version is on TfL’s website, here.

On balance, showing more possible interchanges on the map is a positive change. But it doesn’t negate the need for a fundamental rethink of how the tube map looks and what it is for. And it’s not, I fear, enough to distract from the Crossrail problem.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.