Tap water is basically water molecules with trace amounts of natural chemicals in it, like calcium, sulphates and chlorine.  We spend a lot of time and effort getting the nasty stuff out and keeping it out before delivering it to the tap.

Does it really matter where those water molecules come from?  What’s the difference between a water molecule that comes from rain, a spring, river, lake, dam or aquifer?  There is no difference. It’s a water molecule – two parts hydrogen and one part oxygen.   Nothing else. Water is life and the Maori recognise this in the Mauri of water.  Without it we will die and reasonably quickly.  However, I believe it’s time for us all to grow up and join the 21st century.  Two hundred years ago, wastewater treatment was rudimentary at best and discharge of raw sewage was common. 

The Maori tradition of discharging to land was very sensible as it stopped pollution of the waterways and offered some natural treatment of effluent.  We don’t discharge raw sewage anymore. You might be surprised to know that the liquid discharged from your local sewage works is about 99.99% water.  That’s the same stuff as before – two hydrogen atoms and one oxygen atom. In London, by the time the River Thames gets to the Thames estuary, the water has been treated for drinking seven times and discharged seven times.  What that means is that if you add all the abstraction from the Thames for drinking water supply, that amount would be about seven times the river flow.  The water taken at one point is that which has been discharged upstream.  London could not survive without recycling its wastewater.  In major cities around the world this practice has been carried out for centuries some times to the detriment of both the natural environment and the health of the consumer.  However, on the environmental side, the Thames now has significant fish migrating up and down it and is recovering from 300 years of abuse.

There is another problem. In New Zealand, we have to discharge our wastewater to land because of the cultural veto.  This is not sustainable.  As our population grows  we are  going to run out of land area to irrigate.  Not to mention that Fonterra will not allow municipal effluent to be used on its dairy land.  This is entirely due to the perception of the practice being unacceptable not just to New Zealanders but also overseas.  We must find new ways of disposing of our wastes.  There are only three places we can dispose of waste, in water, in/on land or in the air.  When we run out of land, we are left with water or air.  Evaporating the waste into the air seems fairly energy intensive and produces a major greenhouse gas – water vapour – probably not ideal.  So that leaves us with discharge to water. I am not advocating that we dump raw sewage in our rivers and streams. Far from it.  I am calling for appropriate treatment and discharge to the local waterway as a sustainable way forward.  Because something was right 200 years ago, does that make it right now or should our ideas grow up with our technology?

This thought leadership article is by Iain Rabbits, a senior water specialist engineer at Harrison Grierson.

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