The proportion of salt to water is very important. We use one rounded tablespoon of salt to every 40 fluid ounces (1.2 litres) of water. Although the fish or piece of fish should be just covered with water, the aim is to use the minimum amount of water to preserve the maximum flavour, so therefore one should use a saucepan that will fit the fish exactly. An oval cast iron saucepan is usually perfect.