Water Quality & Water Supply: Definition & Purpose

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Learn the difference between water quality and supply, including the factors that make up good quality of water, and why it's important for humans and other animals alike. Check the quality of your learning by finishing with a quiz.

Why is Water Important?

Water might not seem like much: relatively tasteless, made up of simple molecules of two hydrogen atoms, and one oxygen atom. But for humans, nothing is more important. You can survive a painful 3 weeks without food, but go 8-10 days without water and even the hardiest humans will perish. Most will barely make it 3 days.

So it makes sense that we should care what our water is like. Does our water contain toxic chemicals? Run off from agriculture? Is it too salty? Is it clear or cloudy? All these things could impact both our health and our enjoyment of the water we drink, and are important to consider. And for those reasons the quality and supply of water we have is really important.

What is Water Quality?

Water quality are measurements of the characteristics of water, which can include chemical, biological, physical, and radiological characteristics. This is usually measured relative to human needs, though it can also be looked at in terms of how the quality of water affects animal and plant ecosystems.

There are lots of things we can measure that forms part of water quality. Let's discuss a few of the most important ones in more detail.

  • A water sample's pH is a measure of how acidic or alkaline the water is. Good quality water should be close to neutral, which is a pH of 7. Numbers bigger than that are alkaline, and numbers smaller than that are acidic. Strong acids are caustic, and strong alkalis are corrosive. Acids burn away at your tissues and cause pain, where as alkalis get absorbed into tissues, but either way they cause a lot of damage. Neutral water is easier for the body to handle. If a water's pH is off, it's because of other things being mixed in the water. Slightly alkali water is usually due to minerals and is probably fine.
  • Heavy metals are metals that have high densities, and usually refers to toxic heavy metals like cadmium, mercury, arsenic and lead, that have got into the water due to nearby factories or old lead piping. These toxic materials are really bad for you, so it's important that water contain as few of them as possible. Your body has to work hard to filter them out and avoid them killing cells.
  • Radon is a radioactive element that is bad for humans, and can sometimes be found in water supplies. Some radioactive material is natural because it's found in many rocks underground, and this especially happens when water is supplied from underground. Radon can cause the development of cancers in humans, and so is best avoided.
  • Drug content refers to the amount of pharmaceutical drugs found in the water. These can find their way into water supplies due to factories pumping waste products into the water, and due to farmers giving drugs to their livestock. They have all kinds of mixed effects on humans which are often poorly researched and hard to predict.

There are other indicators that might be important in terms of the health of non-human ecosystems too, like turbidity (transparency), dissolved oxygen, suspended solids, temperature, and presence of particular kinds of bacteria.

Turbidity and dissolved oxygen are two measures that are particularly important for water-based animals.

  • Turbidity is a measure of how clear the water is: how many particles like sand, silt, clay, algae and others are found in the water. Some animals prefer clearer water, and some are healthier in cloudy water. Humans prefer their water clear, and most governments have rules on how cloudy water can be.
  • Dissolved oxygen is mostly about non-human animals, and determines how easy it is for fish to breathe through their gills. Entire populations of fish can be killed if dissolved oxygen gets too low: dissolved oxygen varies with temperature, water speed and roughness. Since we don't breathe water, it doesn't really affect us, though we do find water high in oxygen to taste better. Most human water supplies are low in dissolved oxygen because it damages water pipes over time.

Turbidity is How Clear the Water Is
Turbidity is How Clear the Water Is

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