Jersey Water could have to start importing water to the island by tanker from Norway if the dry spell continues.
Managing director Howard Snowden urged islanders not to waste water as supplies were low.
The reservoirs are 35% full, and the desalination plant is running on full power, but it is only able to produce 30% of the island's daily demand.
Mr Snowden said: "We cannot emphasise enough to everyone how important it is to take these warnings seriously."
October and November are normally the wettest months of the year in Jersey, but so far only 2 inches of rain have been recorded which is less than a quarter of the average rainfall for this time of year.
Mr Snowden said: "We were in contact with a company some years ago which specialises in moving water, particularly to island jurisdictions where they're struggling.
"They've got a tanker that would ship about 90 million litres of water, that's about six days' supply, and offload it within a week."
Jersey Water said long-range forecasts suggested no significant rain was expected in the coming weeks.
The firm has begun a public campaign advising islanders about how to save water.
The company has also urged islanders to look out for leaks and overflows and is asking businesses to cut down on non-essential water use.
But Mr Snowden said: "If the unusually dry and settled weather at this time of year continues without significant rainfall, we will have no choice other than to implement formal restrictions on non-essential uses of mains water.
"Part of the contingency plans also include importing water into the island by tanker; therefore we are asking everyone to help reduce the demand for water now by being conscious about how much we all use.
"Restrictions would also apply to commercial customers, whom we are also urging to reduce their use of mains water wherever possible."