How long does the water cycle really take?

We all know the drill: surface water is evaporated into the clouds and then the moisture condenses and forms rainclouds, which eventually precipitate (rain, sleet, hail or snow) the water back down to the reservoirs we utilize for drinking water. From there, the water is filtered and treated and then transported to us through pipes and taps. Our bodies absorb the water and eventually release it back to the ground, oceans and reservoirs, where it embarks on the journey all over again.

It seems like a pretty good system, and it is! So, if all the water comes right back to us, why are we so worried about conserving water? Well, there’s something missing from this water cycle story and that’s how long it really takes for the water to make that journey. Maybe you've heard that only 2% of the world's water is available as fresh water. What you may not know is that most of that fresh water is in the form of glaciers and ice sheets. A much smaller percentage, around 0.03–0.01%, is stored in reservoirs like lakes and rivers and is available for human consumption. This comparatively small amount of fresh water is used for eveything we do from taking bubble baths, to flushing the toilet and making iced tea to more polluting uses like producing meat, making plastics and all other forms of industry. Because we use water for so many things and there are so many water-loving organisms in the world, water protection and conservation is an important message to spread.

So how long does each stage take before it goes to treatment?

Atmosphere: Water is in the atmosphere for a just around nine days; this is the briefest visit water will make on it's journey through the cycle

Ground: When the water precipitates to the earth, it can stay in a few places. If it comes to the ground, it will likely hang out there for a month or two, though some of it will trickle down as shallow groundwater, where it can stay for 200 to 300 years. Deep ground water can remain underground for 10,000 years. 

Snow and Glaciers: Water could come back down to earth as snow cover instead, where it could remain for two to six months until the spring melt. Glaciers trap that fresh water for 20 to 100 years.

Ocean: Water can also end up in the ocean, where it could stay for over 3,000 years!

Ice shelf: If water makes its way to an ice shelf like in Antarctica, you can just forget about it. If all goes well, that water could be there for 900,000 years.

Before you can drink it, the water needs to goes to a treatment facility where it is put through a comprehensive treatment process: 

Pre-chlorination: for algae control and stopping any biological growth

Aeration: works alongside pre-chlorination for removal of dissolved iron and manganese

Coagulation: a substance is added to achieve flocculation (clumping of sediments so they are easier to filter)

Sedimentation: for solids separation, that is, removal of suspended solids trapped in the floc

Filtration: removing particles from water

Desalination: removing salt from the water

Disinfection: for killing bacteria

And that’s not the end of it!

Once the water has made a journey around the cycle and through the treatment process, it has to find its way to your house through the water mains, pipes and plumbing. How long it takes for water to travel to and from treatment facilities to your house depends on where you live and how far away your nearest water treatment facility is. Do you live on top of a hill or mountain? Water could take extra time and energy to reach you. Some people live many kilometres away from a treatment facility, so the water would have to travel a great distance to get to their taps.

So, the water cycle is a little more complex than you might have imagined and, since we only have access to less than 0.03% of the world’s fresh water at a time, remember to use it sparingly.

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If you want to learn about water usage and how to conserve water?

Visit BC Waste & Water Association, "the people who keep your water clean and safe." Science World's Resources activities Water Savers and Wonderful Water will also help you explore these concepts further.