The hippo in the room

This is about water. Or rather, our impending lack of it. (“Elephant in room” -> “hippo”: another big African mammal, the hippoPOTAMUS, “horse of the river”, one that suffers dreadfully at times when water is scarce. (Yes, I forgot to take my pills this morning.))

Two challenges for you…

a) How much water do you use?

b) What is “your share” of all the water that is available?

Are you using more than your fair share?

How much water do YOU use??

Even if you only add up the obvious things, you will have made a start.

We’re looking for how much water you use per day, on average.


Don’t forget the water you use every time you flush a toilet, though. (Scary: In some much of the world, safe drinking water is precious, a life and death issue. In many of the homes of people reading this, we don’t give a second thought to turning safe drinking water into something you wouldn’t want to drink. Could we not somehow fill toilets with the water from showers we take, from the water that leaves washing machines?

(Note that the water to wash you, your clothes, your dishes should be included in “the water you use”.)

How much water you use is, by the way, an “economics” question. Did you ever think of “economics” like that before? (I hope not. I hope these pages give you Things You Never Thought Of Before.) (The water you use is just a small element in an analysis an economist could make on water usage. Try to “forget” about money when trying to understand “economics”. If you are studying where a scarce commodity (water, grain, labor, coffee, computer chips… etc) comes from, where it goes, who has it, who wants it… then you are working doing economics research. (Of course money comes into it… but it isn’t at the heart of it.)

(Jump down to “What is your share of the available water?” if you aren’t mesmerized.)

How much water do you use?… do you ride in a car or a bus? That car or bus will need water for the windshield washer. If it is your family’s car, and you are a family of three, and a liter of water is put in the tank every month, then it seems “fair” doesn’t it, to say you “use” 1 litre/3/30 per day?

What about the big vehicle that delivered the gas to the gas station? Its windshield washer needed water too. Now… your “share” there will of course be very small. But maybe you begin to see how “the water you use” is not a simple thing?

Now… you add water to the windshield washer quite often. Often compared to how often you buy a car. But making a car takes a great deal of water. (I can defend that… do you want me to start? No? Then you have to agree to accept what I’ve said!)

Let’s say it takes a thousand liters of water to make a car. And that you buy one every 5 years. And that the sort of car you buy will be used by three owners in its lifetime of 10 years. More mathematics! But you can agree, I hope, that “you” “used” at least some of those 1,000 liters?

The food you eat…

Let’s say you live on a diet of tea, lettuce, and chicken nuggets.

You use water to make the tea. The farmer uses water to grow the lettuce. The chicken must have water and grain in the weeks before it becomes nuggets. The farmer that grows the grain for the chicken needs water for THAT. And all the vehicles involved (well, most of them) need water for their windscreen washers… and needed water to be built.

I would argue that “you” have used at least a share of ALL that water! Yes, of course: If the farmer growing your lettuce used 500 liters to grow 5 heads of lettuce, and you only bought one of the five, then you “used” only 100 liters… I’d even let you cut that back some because I’d say the farmer used SOME because what you paid to buy the lettuce was profit for the farmer. He/she “used” the water that led to the profit, I would say. (Do you know the profit margins of farming? Less than 10%. (Much less, often.) Let’s say the lettuce cost you $1. If so, the farmer had to SPEND 90 cents to make the 10 cents. So he only “used” 10% of the water to grow the lettuce. (If you want to get REALLY arcane, consider that if the farmer spent 90 cents to grow your lettuce, some of that money was profit for the man that drove it to the grocery store. Let’s say he was paid 5 cents for that… but that it cost him 4 cents to do it. So HE “used” 1/5th of 1/20th of the water. But that water use comes off of the total the farmer “used”, doesn’t it? (Let’s agree not to get really arcane?) (Except to say that if you are, say, the grocer, you have to factor these things into your water use!)

Anything you own or use has water costs.

The two great costs are…

  • The variable costs… like the water for the windshield wipers, and the fixed costs
  • The fixed costs… like the water to make the car

Water use by your home: Let’s say it took 500 pounds of concrete to build your house, and that three of you will live there for 10 years and that the house will last 40 years

Making concrete takes water… Okay, “your” daily share of that water is (the total) / 4/ 3 / 10 / 365… but since “the total” was a very big number, your share of the water for the concrete is not insignificant. Especially when you think about all the other things you really should add to “the water you use”.

(By the way: You’d be amazed at the “carbon footprint” of all the concrete we make. But that’s a different story… but it would go along similar lines if you think about it.)

What is your share of the available water?

One approach to finding an answer to that would start with answers to…

  • What is the total water I am entitled to, including the shares of other entitled people to that water?
  • How many people share that entitlement?

Total water? How about figuring out how much water falls in your local watershed, (Wikipedia link) (Another name for it: drainage basin.)

Start with the area of your watershed. Then look up the cm of rain per year for that part of the world. Do a little mathematics. Job done!

What water is “your” water is actually an explosive issue. The people of California use a great deal of water that first fell to earth in Colorado. But then again people in Colorado eat lettuce grown in California. I hope you can see that an economist could help us with how we would properly account for these matters?

I’m going to stick with my simplistic premise that you have a natural right to the water that fell in your neighborhood. With, perhaps, an allowance for water that fell in “shared” districts, elsewhere. (As long as the people living there get THEIR share, too! We are very good, these days, at taking from the poor to pamper the rich.)

How many people live in the area where “your” water comes from? Not so very hard to determine, is it?

A simpler approach

You can take a simpler approach. Forget watersheds… Just ask “What’s the population in my town/ county/ state… you choose! And what is the rainfall in the area?

But I think that asking about “our” watersheds helps us to focus our minds on what is meant to be at the heart of this: What’s my fair share?

Are you using more than your fair share?

The two numbers we’ve thought about are the ingredients to a very imperfect answer to “Are you using more than your fair share of the available water?”.

But I hope that you will find it useful to have thought about these things with me as you read this.

I have no idea how much water I use.

(The following is not, perhaps, the most direct route to the answer, but I hope that it too stresses the “what is fair” element.)

There IS an error in what I’ve shown! It was genuinely one I made while writing this. Don’t worry if you spot it, I will give you the right answer in a moment! (I knew there had to be an error when my answer by the other method (given later) disagreed badly with my first answer here. I thought I’d leave it as it was, in case it might amuse you to see how long it takes you to find it. There’s just one error… I hope!)

But my local watershed is about 450 km2.

Annual rainfall= about 750mm

Rain / m2= about 0.75 m3.

Rain across watershed= about 750,000 m3.

The population in that watershed is about 120,000 people.

Water per person per year, after you re-do things to get rid of the mistake in the above (!), if the people aren’t taking water from other places… about 2,800 m3… for everything, for the year.

How many “other places” are there where there aren’t already people who think they should have the water from there?

Answer by the “simple” route? And by a different scheme of calculation…

Population of my county: 1.7 million people.

Area of my county: 3,750 km2

Rainfall: about 750mm.


People / km2: 455

Rain / km2: 750,000 m3

Fair share, water / person: 1,650 m3

(I can live with the “discrepancy” this produces. The distribution of the population across my county is not uniform, and my area could be less densely populated than average.) (Although I will admit that I had to change “more densely” to “less densely” to make my statement fit the facts! If we’re in “less densely” populated area… I suppose it is possible… I’d hate to live in a “typically dense” area!)

That seems like a lot of water…

2,000 m3 might seems like a lot of water. But to live for a year on one tank of water, if the tank were “only” 10m x 10m x 20m might turn out to be quite a challenge. Perhaps looking at the first question in this essay has prepared you to see that?

And think what the world would look like if we collected and used all of the water that fell.

The world would probably look “a bit” different”: Everywhere, the rest of the world would be making do with “second hand” water.

The distribution of water would change radically. Water in streams would be the processed water leaving water treatment plants, or say, run off of our cars after we’d washed them. Some of the water in the soil would be water that had “escaped” from the water put on fields by farmers.

It isn’t just humans that deserve a share of the rain that falls!

If you “did the sums” to estimate your water use, I think you’ll find that even if we count all of the water that fell, we wouldn’t have a great margin for increased population or decreased rainfall… Unless we want to live in a very different landscape.