Rates, Unit Rates and the Cape Town Water Crisis

A couple of weeks ago the Cape Town water crisis caught my eye. This is a slightly different article than what Dan Meyer referenced in his post  in that the NBC News article includes a graphic and a link to a water usage calculator.


This was a great opportunity for my sixth grade math students to: 1) explore estimation and rates while examining a real world issue, and 2) ponder what they can do to conserve water. As an aside, the 6th grade team is looking to expand this two day lesson into a larger conservation effort.

PLC tracking document

I began the lesson by asking students how much water they consume in a day. “Six hundred gallons,” one student suggested. “Ten gallons,” said another.

I jotted down their estimates, then asked, “Where are those numbers coming from? Are they wild guesses? How could we possibly make our guesses a bit more informed?”

One student asked, “How do we use water?”

“Great question! In what ways do we use water?”

Students started calling out several uses that were captured on the water usage calculator–bathing, flushing the toilet, hygiene, etc. I then asked, “How much water do you think you use when you shower or flush the toilet? Can you think in terms of liters?” I needed the students to think in terms of liters because the calculator is metric based. Fortunately a student had a one liter Nalgene water bottle on her desk so I held it up for reference.

“Now, open up this document in Canvas and complete the first column, (there were 10 categories). When you’re finished, go to the website and calculate your daily usage.

water estimate

actual amount

At the end of day one students reflected on their estimate vs. actual water usage.


On day two we read the NBC News article aloud in class, stopping periodically to discuss the reading. At the end students again reflected–by describing at least two ways residents in Cape Town are conserving water, along with a closing statement about what you can do to conserve water.


This lesson addressed Dan’s question, “How can we put students in a position to appreciate, replicate, and even adapt those calculations for their own contexts?”

With more time, I hope a future rendition of this lesson will allow students to delve deeper by creating a cross-curricular study focusing on conservation, advocacy, and service.



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