Seven tankers are transporting 200,000 litres of water a day to help meet the increased demand.Read more
Sprinklers have been banned in Alderney to protect water supplies, the island's water board has said.
Staff said residents and gardeners should not use them until further notice "at night or in the daytime".
They said the ban followed "a long period of dry, sunny weather with many people spending more time in their gardens as a result of lockdown restrictions" which had caused a spike in water usage.
Gardeners should "use only a domestic hand-held garden hose", they added.
BBC News Online
Water supplies in the Watford area have been affected overnight as their storage reservoir north of the town ran almost empty yesterday.
Affinity Water said the "the high level of demand" it was experiencing was due to lockdown and more people being at home. A spokesman said the firm worked overnight to restore supplies.
Last week there was a problem with a loss of water supply in Harpenden and Wheathampstead.
Across England, people have been urged to save water as utility companies attempt to meet "sky-high" demand.
In a series of tweets this morning Affinity said: "We are experiencing low pressure in certain parts of our network due to demand.
"With the increase in people being at home and using nearly 50% more water than they normally would when its hot.
"We currently have teams working around the clock to treat the water faster, to get it in to homes quicker, this is the reason for lower pressure."