When Waste Water Enter a River (dilution)

  1. Explain to pupils that wastewater is diluted when it is discharged into a watercourse. What does this mean?
  2. Pour muddy water into four glasses (about 0.5 dl in each).
  3. Add clean water into glasses and mix well the content of every glass:
    • no water added to the first glass: it will be for comparison with others.
    • fill up to 0.1 dl of clean water to the second glass.
    • fill up to 0.5 dl of clean water to the third glass.
    • fill up to 1 dl of clean water to the fourth glass.
  4. Compare the dirtiness of water in all four glasses. What do you notice? (concentration of muddy particles is smaller in those glasses to which clean water was added). You can also define turbidity of your samples by helping yourself with the Activity Water Transparency (visibility).
  5.  Imagine what happens when sewage discharge into a small stream or a large river:
    • How does water from sewage discharge look in comparison to that in a stream or a river?
    • How does water in a stream or a river look after discharge of wastewater in comparison to the water before that point?
    • What are the consequences of diluting properly treated/cleaned or untreated wastewater in a river?



Activity adapted from Vahtar, M., Zdešar, M., Kompare, B., Urbanc-Berčič, O., (2005): Kako se reka očisti? –  Priročnik za učitelje 3. Book collection Vodni detektiv. ICRO Domžale, Domžale, Slovenia, p.36.