Parts of England are in "crippling drought" with some rivers and groundwater levels lower than in 1976, it has been warned ahead of a Government summit on the issue.
The region joined parts of eastern England which have been drought-afflicted since last summer, as two dry winters left some rivers and groundwater supplies at levels lower than 1976.
The drought was declared by the Government as the Environment Department (Defra) convened a summit of water companies, farmers and wildlife groups to discuss potential water shortages in England.
Following the summit, companies in the South East warned that water restrictions such as hosepipe bans may be needed to ensure essential public supplies are maintained throughout the summer.
The spread of drought prompted warnings from green groups that England's water supply system was failing to work effectively to conserve water and protect the environment. And there were calls for householders to save water in the face of the dry conditions.
The water companies said they were "not running out of water", but without a dramatic improvement in the situation, with significant rainfall in the next few weeks, they will have to implement measures to tackle drought.
The South East has experienced the driest October to January in the region since 1992, with around 73% of expected rainfall, the companies said.
Since October 2010, the region has had only four-fifths of the long-term average rainfall, leading to a "huge cumulative shortfall" in the rain needed to replenish the groundwater aquifers that supply much of the region's water.
The lack of rain continued last month, with the South East receiving two-thirds (66%) of the long-term average rainfall for January. In the Thames Valley and London, rainfall has been below average for 18 of the last 23 months.
Speaking after the summit, Environment Secretary Caroline Spelman said: "Drought is already an issue this year with the South East, Anglia and other parts of the UK now officially in drought, and more areas are likely to be affected as we continue to experience a prolonged period of very low rainfall."