BY MORT ROSENBLUM
  Associated Press

  MEXICO CITY - Awash in maps and charts, Mario Cantu Suarez sighed and pointed to a list of 35 cities. All of them, he said, must shrink dramatically unless more water can somehow be found.

  ''We would have to evacuate people,'' he said. ''Without water, it is the only way.'' A forced exodus from parched cities seems far-fetched, and no one suggests it is
  about to happen. But for Cantu Suarez, a deputy director of the National Water Commission, it is a specter haunting Mexico's future.

  At this rate, parts of the country are dying, with fields poisoned by salt and village wells running dry.

  ''We have lots of water in some places but not where the people are,'' Cantu Suarez said.

  Eighty-five percent of Mexico's economic growth and 75 percent of its 100 million people are in the north, and the water is far to the south. It costs too much to send
  through pipes over mountains or to desalinate far from the sea.

  NEEDED ELSEWHERE

  To supply the north's thriving new industries and farms, Mexico depends on much of the same water that is badly needed in California, Arizona, New Mexico and Texas.

  With high birth rates and migration, urban centers all over Mexico are growing fast. Tijuana and Ciudad Juarez, for instance, have gone from sleepy border towns to
  cities of more than one million in a generation.

  A few doors down from Cantu Suarez, a colleague, Cesar Herrera Toledo, worries that Mexico's profligate past has foreclosed its future.

  ''It's the Mexican system,'' he said. ``There was never time to plan or talk about health, and everything got out of hand. Instead of being careful, we just kept pumping.
  Like gold fever, that can happen.''

  Now water is high on the government's agenda, he said, but people continue to think in their old ways.

  The old laws said no Mexican could be forced to pay for water. That rule no longer applies, but politicians facing elections are reluctant to ask voters to spend more on
  any utility, let alone water.

  Agriculture uses 80 percent of the water and pays nothing, although it only ranks seventh in contribution to the gross national product. Households pay less than a third
  of actual cost of delivery. That leaves industry, the backbone of Mexican hopes for development, paying up to five times as much as households.

  POLITICS

  Another part of the problem is politics and bad planning. Even the megalopolis of Mexico City, built eight centuries ago atop vast lagoons, cannot supply water for its 22
  million inhabitants.

  Less than half of the capital's waste water is treated. The rest sinks into underground lakes or flows toward the Gulf of Mexico, turning rivers into sewers.

  Hydrologists estimate that only 27 percent of Mexico's surface water is clean enough for simple treatment. Some 49 percent requires complex and expensive equipment.
  The rest is too poisonous for any practical use.

  Then there is the diplomatic showdown. After years of battling drought, Mexico and the United States must grapple with each other over rivers they share.

  The Colorado, drained by 10 U.S. states, is a muddy trickle by the time it reaches the rich farmland of Baja California.

  Under agreements worked out decades ago, Mexico receives a fixed minimum of the Colorado's normal flow -- more in rare years of excess. But the Rio Grande
  requires complex negotiation. Mexico can borrow extra Rio Grande water, but must pay it back.