Sophie is furious because she just heard the toilet flush.

Her homework for this week involves totting up all the water that our household uses this week - number of baths, number of showers, number of glasses of water drunk, number of pots of tea brewed and so forth. She had just spent half-an-hour working out today's consumption so she can go to bed, and was feeling the satisfaction of a job well done, when she heard the tell-tale "whoosh" and realised that she'd either have to mess up today's beautiful addition sums, or add the extra flush into tomorrow's total.

I think I won't tell her that I am about to brew a pot of coffee.