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Mellow Yellow - Teacher Notes

Mellow Yellow

In California, when the state was facing a drought, everyone was encouraged to think

'Mellow Yellow'.

Mellow Yellow is 'never flush the toilet if you just pee'.

If everyone in California did this, how much water would be saved?

Teacher Notes for Mellow Yellow

Stucturing the Activity

Decide how much support you will give to students, and format the task appropriately.

This task is suitable for homework.

Pupils need to know the number of people in California, and the capacity of a toilet cistern.

They can be asked to find these things on the web, or you can give them the information at the start (see below).

Solution for Mellow Yellow

water saved = number of flushes for urine only per day * number of people * cistern capacity

We need to know each of these values.

The cistern capacity can be estimated by finding values on the www.

An old cistern will use about twelve litres of water per flush.

A more modern cistern is likely to use six litres for a full flush, and three litres for a half flush.

Some new cisterns use four and a half litres for a full flush and three litres for a half flush.

The number of people can be found on the web.

The US Census Bureau offered an estimate of the 2006 population of California as 36,457,549 (downloaded 4 July 2007).

The number of flushes for urine only per day can be estimated by class votes, or by an anonymous survey.

Practical Work

Method 1: Pupils record their flushes the day before the lesson; some anonymous system of collating the results might be appropriate.

Method 2: Ask pupils for a lower bound, then an upper bound for a typical day.