Water ice

Boil drinking water, let it cool, then boil it again before freezing it in a clean tray. This can reduce cloudiness, though a well-insulated container that freezes from the top down works better for making a clear block.

A standard freezer usually takes about three to four hours to freeze a tray of cubes. Leave space between the tray and other frozen food so cold air can circulate.

As water freezes, its molecules form an open crystal structure that takes up more room than liquid water. Leave space in a bottle or container before freezing water, or it may split.

Once frozen, transfer the cubes to a clean, tightly sealed freezer bag or box. Ice can pick up smells from foods such as fish or onions, so keep it sealed and use it within a few weeks for the best flavour.

Put ice cubes in a sturdy, clean tea towel, fold it over, and tap them with a rolling pin until crushed. Work in small batches; the towel helps contain the fragments and absorbs some meltwater.

Ice made from drinking-quality water is generally safe to eat. Use a clean tray and scoop, and avoid handling ice with bare hands if it will go straight into a drink.