It took no time for Tarrant County to learn how big it had lost Thursday in its seemingly interminable dispute with Oklahoma over getting water from north of the Red River.“We hold that Tarrant’s claims lack merit,” Justice Sonia Sotomayor wrote succinctly at the end of the first paragraph of her opinion for a unanimous Supreme Court in Tarrant Regional Water District v. Herrmann.The ruling holds implications for a large swath of North Texas because TRWD serves an 11-county area that includes the cities of Fort Worth, Arlington and Mansfield and gets thirstier as its population continues to grow rapidly.Sotomayor noted that the population of Dallas-Fort Worth increased 23 percent from 2000 to 2010 (from 5.1 million to 6.4 million).“This growth has strained regional water supplies, and north Texas’ need for water has been exacerbated in recent years by a long and costly drought,” she wrote.TRWD has estimated that its clients will need an additional 400,000 acre-feet of water per year by 2060, which makes increasing the supply imperative. (One acre-foot equals about 325,000 gallons.)The long-range plan includes a partnership with Dallas Water Utilities on a pipeline that will haul water from East Texas reservoirs. Construction is scheduled to start this winter and be completed in 2020, according to the TRWD website.But for more than six years, the water district also has been trying to tap up to 130 billion gallons from a Red River tributary through a decades-old agreement.Texas, Oklahoma, Arkansas and Louisiana signed the Red River Compact in 1978, and Congress’ approval in 1980 made it federal law. But since 2007, TRWD and Oklahoma have been fighting in court over whether the pact allows states or their agencies to cross borders to get their share of water.Oklahoma said no because its state laws block any transfer past the river. The water district argued that the compact’s silence on cross-border movement allowed it to buy the water and that the Oklahoma laws unconstitutionally interfered with interstate commerce.The U.S. solicitor general sided with TRWD’s view that it could get water north of the river to secure its equal share, but the justices weren’t persuaded.“States rarely relinquish their sovereign powers, so when they do we would expect a clear indication of such devolution, not inscrutable silence,” Sotomayor wrote.“Adopting Tarrant’s reading would necessarily entail assuming that Oklahoma and three other states silently surrendered substantial control over the water within their borders when they agreed to the Compact. … we find this unlikely to have been the intent of the Compact’s signatories.”Sotomayor, though an East Coaster through and through, showed some appreciation for the long-running southern rivalry.“The Red River has lent its name to a valley, a Civil War campaign, and a famed college football rivalry between the Longhorns of Texas and the Sooners of Oklahoma,” she wrote. “But college pride has not been the only source of controversy between Texas and Oklahoma regarding the Red River. The River has been the cause of numerous historical conflicts between the two States, leading to a mobilization of their militias at one time, and the declaration of martial law along a stretch of the River by Oklahoma Governor ‘Alfalfa Bill’ Murray at another.”But colorful episodes in history aren’t the half of it. In practical terms, the ruling could push other projects, such as building the Marvin Nichols or Toledo Bend reservoirs, up by decades.And don’t imagine that getting those done will be easy, even given crucial needs.Look at the state’s water plan. It took all session for the Legislature to agree on a mechanism for funding what are expected to be $53 billion worth of projects plus $27 billion in municipal needs. Voters will be asked in November to authorize taking $2 billion from the state’s $11.8 billion rainy-day fund into help pay for water projects.But critics hope to defeat that proposal.Water is essential. But getting enough to where it’s wanted won’t ever be simple.