The hosepipe ban will not be lifted despite continuous rainfall since it was introduced.
Lincolnshire supplier Anglian Water says the shortage has been caused by long spells of dry weather and much more rain is needed.
The ban was introduced across many parts of the country on April 5.
Anglian Water spokesman Antony Innes said: "Recent rainfall is a relief for the environment, and no doubt our customers will have found it useful in the garden as well.
"However, we must keep in mind that this drought is the result of almost two years of below average rainfall, including two very dry winters – this is why the region's first hosepipe ban in more than 20 years was introduced.
"It is going to take more than a few wet weeks to reverse the impact of the prolonged periods of dry weather that we have experienced and allow the hosepipe ban to be lifted."