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In the process of studying water security, I’ve come across many definitions of what the term actually means, including gradations between water stress, water scarcity, and absolute water scarcity. Though annual freshwater supplies per capita is only one piece of water security, it’s an important way to measure and compare water security across countries or regions. For simplicity’s sake, I’ve focused on the definitions :

• Water stress: < 1700 m^3/person (449,092 gallons/person)
• Water scarcity: < 1000 m^3/person (264,172 gallons/person)
• Absolute water scarcity: < 500 m^3/person (132,086 gallons/person)

But these definitions are only marginally useful because, to be honest, I have no idea how much water 500 meters-cubed is, and can’t conceptualize what it’s like to use 500 meters-cubed of water divided over a year.

So, in an effort to better conceptualize how much water we’re actually talking about, I decided to track my own water use for a week and compare it to various levels of water scarcity.

Last week, I recorded every time I directly used water – turning on a faucet, flushing a toilet, or drinking a liquid. Here are my daily averages:

• Drinking a beverage: 6 times
• Washing my hands: 7.1 times
• Flushing the toilet: 6.5 times
• Brushing my teeth: 1.7 times
• Showering: 1 time
• Doing the dishes: 1.4 times
• Boiling a pot of water: 0.7 times
• Doing a load of laundry: 0.3 times (2 loads in a week)

Let’s look at each activity and see how much water is used according to the :

• Drinking a beverage: 8 ounces (0.0625 gallons)
• Washing my hands: 1 gallon
• Flushing the toilet: 3 gallons
• Brushing my teeth: < 1 gallon
• Showering: 16 gallons (based on an 8-minute shower)
• Doing the dishes: 8-27 gallons
• Boiling a pot of water: 1 gallon
• Doing a load of laundry: 25-40 gallons

To be honest, some of these estimates are a little strange to me. For instance, an 8 ounce glass is pretty small, and the idea that I’d use a full gallon of water while brushing my teeth assumes I have the faucet on the whole time, as does the high end estimate of dish-washing. But for the sake of argument, let’s assume my beverages are small and I brush my teeth with an open faucet. Furthermore, let’s assume my dish-washing is right in the middle (let’s say 15 gallons), and that my laundromat has a relatively efficient machine (let’s say 30 gallons per load).

So based on my daily usage, here’s how much water I used each day by each activity:

• Drinking a beverage: 3.75 gallons
• Washing my hands: 7.1 gallons
• Flushing the toilet: 19.5 gallons
• Brushing my teeth: 1.7 gallon
• Showering: 16 gallons
• Doing the dishes: 21 gallons
• Boiling a pot of water: 0.7 gallons
• Doing a load of laundry: 9 gallons

That’s a grand total of 78.75 gallons of water per day. Over the course of a year, that would be 28,744 gallons of water, or 109 meters-cubed. (If you’re interested in doing your own calculations, here’s a pretty good .)

109 m^3 per year doesn’t seem too bad considering that the United States has 9,666 m^3 of renewable freshwater per person per year. I certainly wouldn’t want to live in Kuwait, which only has about 5% of my use rate available per person, but as long as I don’t live in one of the with fewer than 100 m^3 of renewable water per person, I should be fine, right?

The problem is that calculating my direct use of water is misleading. It doesn’t take into account the water needed to grow the food I eat, cool the thermal electricity plants that power my appliances, or produce the products I use. In fact, in a high-income country like the United States, domestic water use only accounts for 11% of total water use. The majority of water is , mostly in cooling thermoelectric power stations. In lower-income countries, domestic water use accounts for just 8%, while agriculture accounts for more than 80% of water use, mostly through irrigation.

My measly 109 m^3 of water per year may not seem like much, but in reality it’s probably only one-tenth of the water use I benefit from on a daily basis. In 2010, the United States used , the equivalent of 1,112 gallons per person, or 4.2 m^3 of water. Over the course of a year, that’s 1,533 m^3 of water per person, more than the amount of renewable water available per person in South Korea or Denmark.

And even that understates how much water I’m using every day because so many of the foods we eat as Americans are imported from other countries. By outsourcing much of our food production, we’re also outsourcing much of our water use. A by two Dutch professors, M.M. Mekonnen and A.Y. Hoekstra, looks at each country’s water footprint – the amount of water needed to produce the good and services consumed by the people of that country. According to their methodology, the uses 2,837 m^3 of water per year – 67% more than the amount of water available in a water stressed country.

Water security is both hard to measure and hard to define precisely because so much of the water we use doesn’t come out of a faucet. Not having enough water resources is dangerous not because I might have to take shorter showers or drink fewer cups of coffee each day, but because it limits our ability to grow food and generate electricity. That’s where most of our water use is happening, but it’s rarely what we think about when we think of water use.

Furthermore, our water use isn’t just happening at home, much of it is happening abroad, in the fields of the world’s big food producers. Countries with very little water like Kuwait are able to survive not because they’re great at conservation, but because they’re rich enough to import most of their water in the form of water-intensive food and industrial products. As global warming reduces the amount of freshwater available in many parts of the world, the price of water will increase – not just in terms of what our utility companies charge us, but also in the form of products that require water in production.

Standardized definitions of what classifies water stress or water insecurity are valuable, but they’re incomplete. Water security is ultimately not just about whether water comes out when you turn on your faucet, but whether you have the access to and means to afford other forms of water, too.