Purify water from a muddy pond in order to survive! 

The open-ended nature of this investigation makes it flexible enough to be used with different age groups (see below for how to use with primary learners). Explore separation techniques and potable water, develop skills in scientific enquiry – and show learners that chemistry is fun. 

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The investigation with student sheet is available as a pdf or MS Word document. For background information and more support with running practical problem-solving investigations in the classroom visit How to use these resources.

More fun practical investigations from our In search of solutions collection.

The investigation

Water for survival

You are on a ‘Survival’ Course, your group has been left in the ‘wilds’ for a few days with only a limited amount of water and food. It is a scorching hot summer’s day. Early evening you discover that the person carrying the water has drunk it all and there is only powdered potatoes or packet soup to eat. Clearly, in order to eat and drink tonight you must obtain some water. Luckily you come across a muddy pond next to a rubbish tip. Fortunately, you also notice old bits of laboratory equipment in the rubbish tip. There is a wood fire beside the pond with charcoal in it.

Your task

Obtain some pure water in order to prepare a meal and to have water to drink the following day. You must also find a way of showing that the water is pure.


100 minutes (this time can be split into a 30 minute planning lesson where students have all the apparatus available to look at, and a 70 minute practical session).

Group size


Equipment & materials

Eye protection.


Glass beakers (100, 250, 400 cm3), large plastic trays, test tubes, boiling tubes, test tube holders, conical flasks and bungs to fit them with a glass through tube (or side-arm flasks or side-arm boiling tubes), straight and bent glass tubing, rubber tubing (5 cm and 30 cm lengths), funnels, filter papers, plastic sieves, glass droppers, evaporating basins, thermometers, paper towels. Bunsen burners, tripods, gauzes, heat- resistant mats, clampstands.


Per group

‘WATER SAMPLE FROM MUDDY POND’: tap water (400 cm3) mixed with soiI (about half a handful), green ink to colour noticeably + salt (4 g) mixed.

Health & Safety notes

This is an open-ended problem solving activity, so the guidance given here is necessarily incomplete. Teachers need to be particularly vigilant, and a higher degree of supervision is needed than in activities which have more closed outcomes. Students must be encouraged to take a responsible attitude towards safety, both their own and that of others. In planning an activity students should always include safety as a factor to be considered. Plans should be checked by the teacher before implementing them.

You must always comply with your employer’s procedures and in some cases may decide that a particular activity is inappropriate in your situation. Further information on Health and Safety should be obtained from reputable sources such as CLEAPSS in England, Wales and Northern Ireland and, in Scotland, SSERC.

Check students’ apparatus before they start heating. Remind students that if their water boils too vigorously they are to turn down the flame. Small blue flame only required.

To avoid the (remote) possibility of infection from soil organisms, it is preferable to heat the soil in an oven first to sterilise it. (In case there is a temptation to taste the water in advance). If using compost, be careful it is not too dry to avoid the possibility of inhaling fungal spores.

Eye protection when boiling liquids.

Warn students that tasting it is NOT an acceptable way of showing the water is pure.

It is the responsibility of the teacher to carry out a suitable risk assessment.

Possible approaches

Fits in well with classwork on evaporation and condensation. Some help on cooling steam may be necessary. Pond contents could be varied, for example oil could be added to the water.

Suggested write-up

Student to write a diary entry for day 1 of the Survival Course (as part of the ‘Survival Course’ assessment procedure).

Evaluation of solution

These are suggestions only:

1 Firstly judge against students’ criteria for success.

2 That some purification was achieved.

3 Does method take into account soluble impurities as well as insoluble impurities?

4 Some tests done on water (visual + boiling point + others).

5 Distillation.

Extension work

Students find out what is in pond water.

Additional resources

  • Create context with scientific research using this starter slide with questions: How ancient Maya peoples made potable water.
  • Link to careers with this video profile of a laboratory analyst and higher degree apprentice who tests drinking water for 15 million people.
  • Develop literacy and trigger discussion with these differentiated DARTs (Directed Activities Related to Text) based on waste water treatment.

For primary science

If you teach primary science, see the headings below to find out how to use this resource.

Our Kitchen to classroom video How to purify water demonstrates a simple approach to purification that can be used in a primary classroom. The life of water resource offers supporting videos and more experiments for primary learners.

Skill development

Learners will develop their working scientifically skills by:

  • Drawing conclusions and raising further questions that could be investigated, based on their data and observations.
  • Using appropriate scientific language and ideas to explain, evaluate and communicate their findings.
  • Asking their own questions about scientific phenomena.

Learning outcomes

  • Observe that some materials will dissolve in liquid to form a solution, and describe how to recover a substance from a solution.
  • Use knowledge of solids, liquids, and gases to decide how mixtures might be separated, including through filtering, sieving, and evaporating.
  • Identify the part played by evaporation and condensation in the water cycle and associate the rate of evaporation with temperature.
  • Observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius.

Concepts supported

  • That knowledge of the properties of different states of matter and how separation techniques can be used to solve real-life problems.

Suggested activity use

This activity provides a good problem solving context for learners to explore using their knowledge of separating mixtures. Learners could work in small groups to share their ideas and carry out the activity, whilst also evaluating their methods, discussing how to improve them.

Practical considerations

You will need to provide the equipment and resources listed in the activity, including pond water, which will need be prepared beforehand. Many of the resources listed are available only in a secondary school, but there are alternatives, such as using heat stands and tea light candles instead of Bunsen burners and tripods.

Previous work on separating techniques would be beneficial, so children can call upon prior knowledge.