Wastewater audit

How much wastewater does your household make?

Have you ever wondered what's in the used water that leaves your home? Doing an audit will help you discover how much wastewater you make, what's in your wastewater and how you can make a positive impact on the quality of the used water that goes into the wastewater system.

Set goals

Think about some goals for your wastewater audit.

Some goals might be:

  • learn about how much wastewater you and your family make
  • identify common pollutants in your wastewater.

How much wastewater do we make?

Did you know that about 70% of the water we use at home ends up being wastewater?

You can find out more about water use and conservation and find out how much water you use at home and at school.

What happens to wastewater?

Wastewater is 99% water. The remaining 1% is made up of things you've added to water as you've used it.

We collect wastewater and treat it so that it's safe to reuse or release to the environment.

You can learn more about wastewater treatment and water recycling.

Make a plan

Follow these steps to make a plan to do your audit:

  1. Do a risk assessment for your wastewater audit. Think about all the things you'll do and how you can do them safely.
  2. Think about how you'll do your audit. Will it be for one day or over a week? Will you do it on your own or as part of a group?
  3. Gather the things you'll need.

Things you'll need
You'll need the Wastewater audit recording sheet (156KB), something to write on, a clipboard and a calculator.

How will you do the audit?

It's up to you!

You can use your own recording sheet to record throughout the day. Or, you could place a recording sheet in the bathroom, kitchen and laundry room and have the whole family help.

How will this change your results? Can you rely on your family to record accurately? How could you check?

You might do it on just one day or you might do it for a couple of days.

How might this change your results? Would the waste be different on a weekday compared to a weekend? Why?

Do the audit

When you do your audit, follow these steps and your plan to find out what's in your wastewater.

Gather your plan and your equipment.

Use the Wastewater audit recording sheet (156KB) to fill in information about the kinds of things being put down the drains in your home.

For each item, record how often and how much waste is disposed of (estimate), and the total weight of each waste in grams.

Read your water bill (320KB) or use the water use and conservation information to estimate how much wastewater you and your family make at home.

Record every time you add something to water, like washing up detergent.

Did you know?
About 70% of the water that comes into your home ends up leaving as wastewater!
You can estimate how much wastewater you make by multiplying your daily water use by 0.7.


Review findings

Analyse your data

1. Calculate your total amount of waste in grams.
2. Calculate the amount of waste as a percentage of the amount of wastewater made. On average, wastewater is about 99% water and 1% waste – was yours similar?

Amount of waste as a percentage of total wastewater






Total waste in one day (from your audit)

Amount of water used in one day

Estimate amount of wastewater made in one day (B x 0.7)

Converted to grams (C x 1,000 g)

Amount of waste as a percentage of wastewater (A / D x 100)







Present your data

How could you present your data in a meaningful way?

You might like to:

  • make a pie graph to show which items you used most
  • make a bar graph that shows which room (bathroom, laundry or kitchen) or drain (toilet, shower, sinks) had the most waste
  • create a class data set with other students. Compare your results.

Review your results

After you've looked at your results, ask yourself:

  • What items did you use the most?
  • What items surprised you and why?
  • What items shouldn't go down drains at all? How should they be disposed of? Learn more about wastewater treatment and what you can do to help.
  • Which items could you eliminate, use less of or substitute for more environmentally friendly options?


Make a change

Find out the many ways you can make a positive impact and spread the word.

Communicate your findings

There are lots of ways to share your findings from the wastewater audit with your friends, family or school. You could:

You might like to try some Persuasive techniques (2.6MB) to encourage people to do the right thing.

Teacher resources

This wastewater audit fits well with Stage 6 Chemistry – Module 1.

Teacher lesson plan – wastewater audit (214KB)

Wastewater audit recording sheet (157KB)

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