Bristol Water has revealed that Mendip reservoir levels have continued to fall due to dry weather.
The firm said levels were now 8% lower than last year despite 2010 seeing significantly low levels which fell below average over seven months.
So far the rainfall levels recorded are only 40% of the normal levels.
The company said it has increased efforts to advise customers how to avoid wasting water and is offering them free water-saving devices.
A campaign has been been launched to persuade customers to think twice before watering their gardens.
'Waste of water?'
Jeremy Williams, from Bristol Water, said: "With good weather and Bank Holidays, the garden-watering season has begun in earnest.
"But just how much of it is really necessary - and how much of it is a waste of water and effort?
"We ask gardeners to stop and think before reaching for the hose or sprinkler, especially during times of peak demand," he added.
In order to combat this the company reduced the amount of water taken from the Mendip sources as much as practicable, replacing this with pumped transfers of River Severn water from Sharpness.
The water company said that it is not short of water and they are not currently planning any water use restrictions.