Purify water from a muddy pond in order to survive

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.


  • Eye protection
  • Glass beakers (100, 250, 400 cm3)
  • Large plastic trays
  • Test tubes
  • Boiling tubes
  • Test tube holders
  • Conical flasks & bungs to fit them with a glass through tube (or sidearm flasks or side-arm boiling tubes)
  • Straight & bent glass tubing
  • Rubber tubing (5 cm & 30 cm lengths)
  • Funnels
  • Filter papers
  • Plastic sieves
  • Glass droppers
  • Evaporating basins
  • Thermometers
  • Paper towels
  • Bunsen burners
  • Tripods
  • Gauzes
  • Heat-resistant mats
  • Clamp stands
  • Charcoal
  • Water sample from ‘muddy pond’

Health, safety and technical notes

  • Read our standard health and safety guidance here
  • Always wear eye protection. 
  • Wear clothing protection if desired. 
  • This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
  • Remind students that if their water boils too vigorously, they are to turn down the flame. Small blue flame only required.
  • Keep a close eye on students working with an open flame. 
  • To avoid the (remote) possibility of infection from soil organisms, it is preferable to heat the soil in an oven first to sterilise it.
  • Warn students that tasting it is NOT an acceptable way of showing the water is pure.

Procedure for technicians

To prepare the ‘muddy water sample’ you will need to mix: 

  • Tap water (400 cm3
  • SoiI (about half a handful)
  • Green ink to colour noticeably 
  • Salt (4 g)  

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. More advice on how to use these resources can be found here

Possible extension

Learners analyse the pond water sample to determine the contents.