As Britain's first drought order in a decade comes into force in south-east England, forecasters are predicting a summer of water shortages.
From banning car washes to standpipes in the streets, there is a range of measures water companies can take to ensure supplies do not run out.
What are the different levels of restriction and what effect will they have on daily life?
LEVEL ONE - HOSEPIPE BAN
Water companies can impose a ban on domestic use of hosepipes and sprinklers.
They do not need permission from the government or Environment Agency to impose a ban.
Businesses such as car washes and garden centres are exempt and hosepipes can still be used to fill swimming pools and hot tubs or wash driveways, patios and paths.
Several such bans are already in force in south-east England.
LEVEL TWO - DROUGHT ORDERS
Water companies can apply to the environment secretary for permission to impose an non-essential use drought order, such as that granted to Sutton and East Surrey Water on 15 May.
Under it, the following could be banned, although companies may choose not to implement the powers in full.
Using sprinklers or hosepipes to water gardens (apart from market gardens), lawns, verges, allotments, parks or sports or recreation grounds, whether publicly or privately-owned
Filling privately-owned swimming pools other than for medical treatment
Filling ornamental ponds other than fishponds
Operating mechanical car washes
Washing cars, boats, trains or aircraft for any reason apart from safety or hygiene
Cleaning the outsides of buildings apart from windows Cleaning industrial premises or plants, apart from for safety or hygiene reasons
Using hosepipes or sprinklers to clean windows
Running ornamental fountains and cascades
Running automatically-flushing toilet cisterns during times when buildings are unoccupied
Separate drought orders can also vary restrictions on the amounts of water the water companies can take from natural sources such as rivers.
If water is running out and there is an exceptional shortage of rain, water companies can apply to the Environment Agency for a drought permit.
This will temporarily allow them to take water from other sources, for example taking more from rivers and groundwater.
The Environment Agency warns that a hot summer could result in one of the most severe droughts in the past 100 years
Southern Water has already been granted a drought permit allowing it to boost its supplies by taking more water from the western River Rother.
The firm was granted a six-month permit in October which has been extended for a further six months.
Sutton and East Surrey Water has also been granted a drought permit allowing it to take water from the River Eden - the two-month permit expires at the end of May.
However, such moves can have potentially damaging effects on the environment.
LEVEL THREE - EMERGENCY DROUGHT ORDERS
Once there is no more water to take from the environment, water companies can apply to the environment secretary for emergency drought orders.
These would allow the use of water to be restricted in any way deemed necessary.
In practice, this could mean:
- Water supplies to homes being shut off and standpipes set up in streets
- Water could be rationed by cutting off supplies to homes and businesses at certain times of day.