Answering a simple question - what is water quality?

The closest things are usually the ones we miss seeing.

Having blogged for 3 years about water quality, it comes as no surprise (or does it?) that I have not talked more about what water quality is.

Let's try to define it. I am a fan of 1-sentence definitions so I shall do the same here. Water quality simply tells you whether the water is suitable for use. Simple enough? Unfortunately, real life often complicates things. For example, what use? For whom (or what)? What is meant by suitable? How to measure suitable? (There goes the 1-sentence rule...)

What use?
These come to mind - drinking, washing, bathing, cooking, swimming, recreation, industry (food & beverage, wafer fabrication, pharmaceutical, cooling water, boiler water...), agriculture (animals, crops...)... The uses of water seem endless and mind boggling. But it doesn't end here.

For whom (or what)?
Environmental science used to be human centric, focusing only on the applications for society and the effects on the human condition. With the rise of the environmental movement, care and concern for non-human entities are increasingly becoming the norm. (I must stress that humans are too part of the web of life so it makes sense to care for these non-human entities. Anything that goes wrong in the environment will ultimately comes back to impact us. Remember - everything is connected to everything else.)

Have you considered the poor fish living in the wild downstream of your wastewater treatment plant? How about that rare aquatic fern surviving precariously in an increasingly polluted river?

Environmental protection and conservation have now come into the picture. Water quality must be of an adequate standard for organisms (especially aquatic ones) to survive and thrive. As someone pointed out, good water quality is not enough to nourish the ecosystem, you need to adopt a holistic view and protect/conserve the rest of the ecosystem too.

But before we get too carried away, don't forget the mind boggling uses of water listed at the beginning. There are many perspectives to water quality. The key is to first define the use for that water. Drinking water will have rather different requirements compard to industrial and agricultural water. Water quality for human consumption can be quite different from that for a fish or frog.

Just as water quality is only one of the many components of conservation, conservation is too only one component of water quality. You may protest, "what has happened to the 'nature conservation' given in your blog profile?" Nothing has happened. I still believe in conserving nature. But realise that water quality is a big topic, encompassing many different viewpoints that sometimes do not fit in well with one another.

What is meant by suitable? How to measure suitable?
This could be a can of worms so I will try not to open it (at least not in this post). Suitability is described by the various water quality parameters (dissolved oxygen (DO), pH, turbidity, metal content, pesticide concentration and many many more). Obviously, the type of use will determine which parameters are important and the limiting values of those parameters. For example, low DO is not a big issue for human drinking except that the water may taste flat. Yet a low DO water can get a fish killed from asphyxiation. Another example - a zero coliform count is expected of drinking water yet a count of less than 200 per 100mL of water is considered all right for swimming.

"Suitability" can be a dodgy term. Yet, I believe that regardless of the inadequacies of water quality parameters and their limiting values, they at least give us a grasp on the elusive nature of water quality and hopefully allow us to work towards better ways of defining water quality.