Science in Action Notes: Fresh & Saltwater Systems (1.0) | Print |
1.0 Humans depend on water supply and quality.
Living systems need water to survive. Ecosystems depend on it. The land is changed by it. Industry uses large amounts of it. Climate and weather are determined by it.
Our 'blue planet' - as viewed from space - is unique among the planets in our solar system, because 74% of its surface is covered by water.

1.1 The Distribution of Water on Earth
The water on our planet exists in many different forms and is evenly distributed over the entire planet.
Drinking Water For HumansDrinking water must be fresh water, not salt water. Not all freshwater on the Earth is drinkable. Water that is drinkable (safe to drink) is called
potable water.

Water On Earth
To put this into perspective:

Water source


Percent of total water

Potable, or not?




Icecaps, Glaciers



Ground water


Fresh - but not entirely accessible

Fresh-water lakes



Inland seas



Soil moisture


Indirect access



Indirect access




Total water




watershed (also called a drainage basin) is a region of interconnected rivers and streams.

Watersheds In Canada
Canada has
9% of the world's freshwater.

A reservoir is an artificial lake.
It is used for storage and management, because many of the larger populated centers in Alberta are far from major river systems.

Watersheds In Alberta

There are 7 major watersheds,
or river basins, in

Peace/Slave River Basin
Athabasca River Basin
Hay River Basin
Beaver River Basin
North Saskatchewan River Basin
South Saskatchewan River Basin
Milk River Basin

1.2 Water Quality
Water quality describes how pure (clean) the water is. Water quality can be measured by the types of substances that are found in it; including living organisms, organic material, minerals and other chemicals. Check out the source to tap story that traces the movement of water in the environment:

Substances Dissolved In Water
Many different substances can be present in water. Most substances that are found dissolved in water are salts. The most common salt is sodium chloride (table salt). The total amount of all salts found in water is called salinity. Saltwater (found in oceans) has a higher salinity (average of 3.5%) than freshwater.

Hard Water
Water described as "hard" is high in dissolved minerals, specifically calcium and magnesium. Hard water is not a health risk, but a nuisance because of mineral buildup on plumbing fixtures and poor soap and/or detergent performance.

Organisms In Drinking Water
Fresh water ecosystems usually contain a wide variety of life forms and organic matter including bacteria - like Escherichia coli ( E coli ) is a type of microscopic bacteria that can cause sickness and even death., fungi, and protozoans; bottom-dwelling organisms such as insect larvae, snails, and worms; free-floating microscopic plants and animals known as plankton; large plants such as cattails, bulrushes, grasses, and reeds; and also fish, amphibians, reptiles, and birds. Viruses are also a significant part of the microbial ecology in natural waters and have recently been shown to play an important role in the nutrient and energy cycles.

Water Quality Testing
Water that comes from deep below the ground is protected from pollutants. However, most cities and towns get their drinking water from surface water sources (lakes and rivers). The water they use needs to be filtered and treated with chemicals.

Water Testing Criteria
Just looking at water in a glass will not tell you if the water is safe to drink. Smelling it may give you additional information - like it may contain hydrogen sulphide (which is harmful to humans) giving it a rotten egg smell. Ocean water is very clear, but cannot be consumed because of its high salinity. Some of the things to test - to determine water quality - are:
? Taste and odour
? Turbidity (cloudiness) and colour
? Toxic substances and other pollutants
? Bacteria
? Hardness or mineral content
? pH (how acidic or basic the water is)
? Dissolved oxygen level
? Suspended solids (including those floating)
? Dissolved solids

Changing Salt Water to Fresh Water
There are two common processes that can change saltwater into freshwater. These processes are distillation and reverse osmosis.
Distillation - a process in which a liquid or vapour mixture of two or more substances is separated into its parts, by the application and removal of heat.Reverse Osmosis - forces saltwater through a filter (membrane) allowing water to pass but not salt.