Professor Brian Cox visits Mogden Sewage Plant in West London to discover how raw sewage is filtered to produce water that's almost (though not quite) drinkable.

At water treatment plants, rainwater from drains and flushed toilet water from sewers is filtered to clean the water we send out to rivers and seas.

Waste water is sieved, separated, aerated (to encourage bacteria to eat tiny pieces of waste), and filtered again to produce “final effluent” – water that’s clean enough to release into the environment.

Made as part of our Schools Experiments series:
   • Brian Cox School Experiments  

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