The governor of Maryland, Parris N. Glendening, imposed broad water restrictions during the week that will shut off lawn sprinklers and require restaurant patrons who want drinking water to request it.
Virginia water officials immediately criticised the measures as unnecessary, despite Washington's ongoing drought.
The freedom to use water in the Washington area now depends on where you are. In Maryland, the use of hoses to wash cars or fill swimming pools will bring sanctions of up to $1,000, while in the District of Columbia and most of Virginia, there are no restrictions.
At a news conference, Mr Glendening called the water shortage a "crisis", becoming the first governor to impose statewide restrictions to cope with the drought. He vowed to protect the state's water supply by asking residents throughout Maryland to share the pain.
In addition to the ban on most outdoor water use by residents, Glendening ordered golf courses to reduce their water use by 80 per cent. On Wednesday night, restaurants were posting signs telling patrons that water would be served only upon request. And executives at one major food company were delivering memos to 25,000 store employees urging them to save water.
"The Potomac is at a historic low," the governor said. "[Scientists] are telling us they're seeing rocks in the Potomac they've never seen before. Now's the time to conserve the water." But the region's other jurisdictions which also draw water from the Potomac River have come to a different conclusion.
In Washington, Mayor Anthony A. Williams said the city's water supply is sufficient to avoid restrictions, although he did call for voluntary conservation.
Across the river, Northern Virginia water officials disputed the crisis and said that two publicly-financed Potomac River reservoirs, built in the early 1980s for the purpose of avoiding water restrictions during severe droughts, are working exactly as intended.
"It's very difficult to understand why anyone who is elected to serve the interests of a group of people would go out of their way to make them miserable," said Mr Burton Rubin, a Fairfax County water commissioner. Water restrictions in the Washington area "are not necessary and they don't help anybody".
Jennings Randolph Lake, a reservoir on the Potomac in western Maryland, holds 13.36 billion gallons of water and is about 84 per cent full, officials said. Little Seneca Lake in Montgomery County, which has 4 billion gallons, is more than 99 percent full.
The two facilities were built by the area's water authorities for $83 million after the region suffered through serious droughts and mandatory water restrictions in the late 1970s.
With those reservoirs acting as a backup, Rubin and other water officials said, the Potomac River can supply Washington and its suburbs for months, even if the region doesn't get another drop of rain between now and next spring.
Water officials said restrictions that may help in Baltimore and other areas of Maryland make little sense in the Potomac River watershed, because there is no way to get water saved in this region to other areas and other watersheds that need it.
"None of the water utilities that depend on the Potomac are asking for water restrictions," said the executive officer of the Fairfax County Water Authority.
Glendening rejected criticism, saying he was taking prudent steps to avoid a more serious crisis if the drought continues throughout the winter, when the region usually gets more rain. He dismissed the notion that water restrictions might be better imposed selectively across the state.
"We ought not to be dividing the state and pitting one region against the other," Glendening said. "The bottom line is my responsibility to the entire state of Maryland. What happens if we get a dry winter? I'd rather conserve now and keep the water in the reserves than roll the dice."
