9,000 homes are without water after a pumping station burst caused a major electrical fault.
Affinity Water confirmed the incident, with water being fed to parts of Hertfordshire and Essex impacted.
Around 280 streets are thought to be affected, with households noticing loss of water from around 10am.
A team of engineers continue to work on site to repair the damages caused and are expected to issue an update later in the afternoon.
In the meantime, residents are being urged to avoid using their washing machine, dishwasher and any electrical appliances that use water.
If you've been affected find out your water refund rights here
In a statement went on to say: "If you still have water, we recommend you put some in your kettle or fridge for drinking in case your water needs switching off for the repair.
"We’re really sorry about this, we’re working to get your water back to normal as soon as possible."
It said: "The repairs to the water main at the pumping station are progressing well, but there is still much to do to get the site fully operational."
The water supplier promised to provide bottled water for customers on its priority services register, while ensuring local hospitals continue to be supplied with water using tankers.
Essex Conservative councillor Holly Whitbread was among the local leaders to tweet out updates from Affinity as some residents took to social media to complain about having no water.
Click here for a full list of the streets affected.
