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In your article about housework (鈥淕erm Warfare鈥�, 14 January 2017), you said that after washing dishes we should 鈥渞inse with plenty of water, preferably hot鈥�. Why hot? Wouldn鈥檛 it save money if they were rinsed with the cold water that comes directly from the mains?

鈥� While washing-up liquids come in various fragrances 鈥� lemon for instance 鈥� that might flavour a sauce, unless you relish the taste of even unscented detergent then it is best to rinse. 鈥淧referably hot鈥� does imply that using cold water remains an option, but there is one big downside to cold 鈥� and it is personal. Water straight from the mains can be icy cold and prolonged contact with it can be painful.

So hot water is more comfortable. Second, it is less viscous, and more readily runs from the tap and off the dishes with the soapy suds. It also happens to be less dense, so you might even use less water and save money this way.

Third, although dish detergents work by binding with both water and grease to form a soluble emulsion, the emulsion still behaves much like its components. Like the neat detergent, it is more viscous and less soluble in cold water. And like the plain fat, it can congeal when cooled 鈥� especially with fats that are solid at room temperature. Rinse with cold, therefore, and your freshly cleaned dishes could end up retaining an invisible film of grease, or the cold conjugate could start congealing to gum up the waste pipe.

Finally, hot water warms the dishes, encouraging any residual moisture to evaporate and dry off more quickly. The precise temperature at which these effects start to make a difference isn鈥檛 clear. Just don鈥檛 expect me to do the research 鈥� it would be like watching plates dry.

Len Winokur, Leeds, UK

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