Some parts of Scotland need double the “normal” amount of autumn rainfall to return water reservoir levels to what they should be at this time of year.
Scottish Water said maintaining some public water supplies remained a “significant challenge” after the second driest summer in 160 years.
It said it was “unusual” for it to ask customers in autumn to take “simple steps” to conserve water.
Parts of the Highlands, north-east and south have had the driest conditions.
Water is of “moderate scarcity” in much of south-west Scotland and also in the Tweed area, Caithness and the River Ythan’s catchment in Aberdeenshire, according to the Scottish Environment Protection Agency (Sepa).
It said in these areas river levels were low and groundwater levels were continuing to fall, with some places “approaching very low levels for this time of year”.
Sepa said other areas were at “alert” level, and Scottish Water warned reservoir levels were low widely across Scotland.