Turning off the tap while cleaning your teeth and re-using rain water to tend to the garden were other options mooted.
A SEW spokesperson said: “Our surface water reservoirs, Ardingly and Arlington, are an important source of water and are falling quicker and earlier than usual.
“Most of the water in them is taken from the nearby rivers, whose flow is much lower than normal because of multiple heatwaves.
“The reservoirs have not been this low at this time of year since the drought of 2022 and, with more warm weather due very soon, we’re asking people protect resources and keep water use around the home to essential purposes only – namely drinking, washing and cooking.”
They added that the company had “dramatically stepped up” its leak repair programme, on which its spends around £40m a year.