South-east England has had 144 days with little or no rain since January, which is the longest dry period since the 70s, according to Met Office weather figures
Parts of the UK are now under an amber extreme heat warning, with heatwave conditions expected to settle through the weekend.
Temperatures are expected to hit the mid-30s in southern areas, peaking on Friday and Saturday.
The forecast comes after hosepipe bans were issued in southern England, with the country struggling to handle a hot and dry summer.
A historic heatwave caused temperatures to reach 40ºC for the first time in some areas in July, and a lack of rain has caused issues for water providers.
South-east and central southern England saw an average of only 5mm of rain last month, while East Anglia had 5.4mm.
It was the lowest rainfall in July for both areas since Met Office records began almost 200 years ago, in 1836.
Drought is expected to be officially declared on Friday.
How long will the heatwave last?
The Met Office issued an amber warning for extreme heat starting at midnight on Wednesday and lasting until midnight on Sunday.
It covers much of the southern half of England and parts of eastern Wales.
Temperatures are set to rise into the low-to-mid 30s for central and southern areas of the UK.
“Away from the highest temperatures expected in central and southern areas, much of England and Wales, as well as the south-east of Scotland, could still see temperatures widely into the high 20s, with a chance of a few spots seeing temperatures into the low 30s,” the Met Office said.
“Scotland and Northern Ireland will also see temperatures into the high 20s and could reach official heatwave criteria by Friday.”
Met Office deputy chief meteorologist Tony Wardle said: “Heatwave criteria look likely to be met for large areas of the UK later this week, with the hottest areas expected in central and southern England and Wales on Friday and Saturday. Temperatures could peak at 35ºC, or even an isolated 36ºC on Saturday.”
When will it rain?
The good news is there will be some much-needed showers next week, and temperatures will start to drop closer to the average for the time of year but could rise again towards the end of the month.
The Met Office long-term forecast for Monday 15 August to Wednesday 24 August says: “This period will see the breakdown of the hot, sunny and dry weather of recent days, with conditions becoming more unsettled across the UK.
“Showers will spread from the west and south next week, sometimes heavy and thundery, though drier periods with sunny spells are still likely between them.
“At the same time, temperatures will gradually decrease closer to normal for August. Later in the period, the more changeable weather will prevail with a risk of heavy showers or thunderstorms continuing, but clear and dry spells in between too.
“Returning to warm or very warm towards the end of the period for much of England and Wales, perhaps becoming locally hot in parts of the south and south-east.”
When did it last rain in London?
South-east England has had 144 days with little or no rain since January, which is the longest dry period since the 70s, according to Met Office figures.
It has not rained in London at all in August.
Dr Mark McCarthy of the National Climate Information Centre said: “July 2022 has been a significantly dry month for southern England; only 10.5mm of rain has been provisionally recorded on average, less than the previous 10.9mm set in 1911.
“The dominant weather pattern for the month has only allowed interludes of rain into northern areas of the UK, with areas further south largely getting any rainfall from isolated and fleeting showers in a month that will ultimately be remembered for extreme heat.”
Much of the country already has low river flows, affecting the quality and quantity of water, with detrimental effects on farmers, other water users, and wildlife.
Farmers have reported stress to crops including sugar beet and maize and challenges irrigating field vegetables and potatoes. In contrast, the dry weather has severely hampered grass growth, which could hit feed supplies for winter.
Where are hosepipe bans in place?
Southern Water has already imposed a hosepipe ban for customers in Hampshire and on the Isle of Wight, marking its first ban in the region for 10 years.
Welsh Water also announced people in Pembrokeshire would be prohibited from using their hosepipes from Friday, 19 August. Rule-breakers will face fines of up to £1,000 if taken to court.
South East Water will introduce a hosepipe and sprinkler ban for Kent and Sussex this Friday amid a prolonged dry spell and “record demand”.
The company has asked people to report their neighbours if they spot them breaching the newly imposed restrictions. It said it would “take the appropriate action” if residents were “ignoring, knowingly or unknowingly, the restrictions in place”.
Thames Water said that it would forbid the use of hosepipes and sprinklers for its 15 million customers across the south of England “in the coming weeks”.
A spokesperson for the water company said: “Given the long-term forecast of dry weather and another forecast of very hot temperatures coming this week, we are planning to announce a temporary use ban in the coming weeks.
“The timing is not confirmed due to several operational and legal procedural requirements, but we will update our customers, partners, regulators and stakeholders earliest to ensure a coordinated approach.”
Thames Water urged customers “to only use what they need for their essential use” in the meantime.
The ban will affect people in parts of Greater London, Gloucestershire, Essex and Kent.
Severn Trent Water, which provides drinking water to more than 8 million people from Bristol to Humber, has said it will monitor the situation closely.
A spokesperson told: “Our region has seen a dry start to the year, only seeing 67 per cent of the rainfall usually expected between April to June 2022.
“However, there hasn’t been a hosepipe ban in our region for more than 27 years, and as we do every year, we continue to monitor reservoir levels and demand for water closely.”
Yorkshire Water said it was “working round the clock” to ensure taps keep flowing for its 5 million customers.
The company said it has not yet applied for a drought order or implemented a temporary usage ban, adding that both are “tools that we could call on if/when we need to”.
Yorkshire Water has asked customers to let their lawns go brown, not wash their cars for a few weeks and to turn off the taps while brushing their teeth.
Affinity Water, which covers 1.4 million customers in regions surrounding the capital, said it was “closely monitoring the situation”.
“At current levels, we should not need to introduce restrictions this year; however, we are dependent on rainfall over the upcoming autumn/winter period to refill groundwater aquifers for spring/summer 2023,” it said.