The temporary ban is to start for all Oxfordshire residents starting from midnight on Tuesday (July 22).
No date has been given for an end to the ban at this stage.
Customers with the OX, GL, SN, RG4, RG8 and RG9 postcodes are affected.
After the driest spring in over a century and England’s warmest June on record, the Thames Valley area has been placed in ‘prolonged dry weather’ status by the Environment Agency.
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This means there is a heightened risk of drought.
Oxfordshire residents are being asked not to use hosepipes, including for cleaning cars, watering gardens or allotments, filling paddling pools and swimming pools or cleaning windows.
While the ban does not impact businesses where water use is a core part of their purpose, Thames Water is asking everyone across the region it serves to be mindful of their water use.
Someone enjoying the hot weather over the weekend (Image: Ben Birchall/PA) According to Thames Water, water usage in Oxfordshire has been up 30 per cent on days where temperatures are above 25C.
Water abstracted from the River Thames is stored at Farmoor reservoir in Oxfordshire.
If as is expected, the warm, dry weather continues the company anticipates that reservoir levels at Farmoor will continue to drop.
In the Cotswolds, aquifers which feed the River Thames are fast draining and the prolonged low rainfall also limits how quickly they can be refilled, further restricting how much water the company can source for reservoir storage.
A hosepipe ban has been announced by Thames Water (Image: Ben Birchall/PA) Nevil Muncaster, strategic water resources director at Thames Water, said: “This has been a challenging spring and summer with big spikes in customer demand during hot dry days and very little rainfall to replenish local supplies in the Thames Valley area.
“Given the continued warm, dry weather we do not anticipate that the situation will improve any time soon so we have to take action now.
“Every drop of water we use comes from the environment and we have to balance protecting this while taking out the water needed to top-up reservoir levels.
“That is why we have had to make to the difficult decision to implement a hosepipe ban to make sure there’s enough water for customers’ essential needs and to protect rivers.
“While this temporary use ban will only affect customers in certain areas, I want to thank all our customers for their understanding and for their support so far to reduce their water use.
“This includes turning the taps off while brushing teeth, taking shorter showers and letting your lawn go dry.”