Simple. Take a tea bag and kettle and brew tea in a beaker - no milk or sugar - then ask pupils how to get the water back. They really don't know how but when you do ink they don't seem to find this a problem. You then distil the tea the usual way in a leibig condenser and hey presto - water!
The best bit is discussing whether or not you could add the water back to the residue and make tea. Yuk! You can talk about tannic acid and why coffee is OK kept hot but tea tastes foul. You can also talk about tannic acid in peat bogs preserving so-called bog bodies and the process of tanning leather (and tanning your stomach). I find the pupils are far more engaged with this than with distilling ink - and they remember it Carol Ashby-Rudd taught at Avonbourne School in Bournemouth until July and now works as head of education and youth work at the Tall Ships Youth Trust
Now it's your turn
Share your brilliant teaching idea with your colleagues on this page - and we'll pay you pound;50. Just send 150 words (plus details of a useful book or website), including your lesson's subject, target age group and your own name and school to firstname.lastname@example.org