What Another Hundred Million Would Mean

It took the United States:

139 years to get to 100 million people

52 years to get to 200 million

39 years to get to 300 million

It could take as little as 35 years to get to 400 million

(— U.S. Census Bureau and various sources)

If --repeat, if --U.S. population grows by yet another hundred million, it could happen soon, well before 2050, say statisticians.

Another hundred million could also change basic equations in America's democracy:

— A quarter of Americans could be Hispanic.

— White non-Hispanics, who were 7 out of 10 in the year 2000, could well dip to around 50 percent … or just below, becoming only the largest among many racial minorities.

— African Americans would likely increase to 14 percent.

— Asian Americans, 4 percent in 2000, would probably double to about 8 percent.

(Americans overall, at 400 million, would become a solid third most populous, behind only China and India.)

And 2 out of 3 Americans would probably live in the West and Southwest.

But that's only if current birth, immigration and migration trends hold steady, which is subject to unpredictables in social attitudes, immigration laws, economic swings, climate change, and the mysteries of ethnic differences in fertility rates.

Far more certain, if the population increases by another hundred million, say experts, is that Americans will need to develop a new relationship to nature's bounty.

Take water.

We have to, since we are, as the aliens in one "Star Trek" episode so memorably dubbed us, "ugly bags of mostly water."

With bodies that are 70 percent water, the now 300 million Americans are already in serious trouble with this most precious liquid.

"In many parts of the U.S., we are already at the limits our natural water supply," water expert Peter Gleick told ABC News. And as number climbs beyond 300 million, Gleick said, "Changes are clearly needed."

For example, when brushing your teeth, do you turn off the tap between applying the toothpaste and rinsing it off the toothbrush -- or when shaving, while scraping your chin?

It may sound extreme, but that's what they do in Bermuda, where there's never been fresh groundwater and they collect the stuff as rainwater from their roofs.

More Americans may be learning such habits as population rises and there's less water to go around.

Water tables are falling fast in much of the west and great plains as drillers probe ever deeper for something clean and fresh, spurred on by drought expected only to increase in coming decades as snowpack melts out sooner each year, leaving summers much drier.

"But the good news," said Gleick, president and co-Founder of the Pacific Institute in Oakland Calif. "Is that we don't have to deprive ourselves - we don't have to stop taking showers -- and we can still be a lot more efficient with the water we have."

There's Proof We Can Do It -- and Drip Hoses for Your Garden

In fact, over the last 35 years, while increasing by the latest 100 million thirsty mouths, Americans also made an impressive start in water efficiency not only by adopting better habits, but better technology.

"We used to shower with 5-gallon-a-minute shower heads. Now many are 2 gallons a minute, so in one minute you're saving 3 gallons," Gleick said. "Where we took 6 gallons per flush, now the legal standard is only 1.6 gallons."

"We were using 200 tons of water to make a ton of steel, now we use only 5 tons! And we're using far less water to grow far more food," he said.

As the population grows, more gardens will probably use drip hoses that lie on the ground, downward-facing pinholes dripping water straight into the earth right next to the plants -- which takes a fraction of the water used by traditional sprinklers that soak all the ground and lose a lot to evaporation.

In 1960, none of California's vineyards used drip hoses. Now 70 percent have them.

So far, Americans have managed to lower the gallons of water per person per year from a peak of 708,000 in 1975 down to 547,000, according to U.S. government figures.

More of Us Means More Expensive Water … and Big Macs

It's not only the price of water that will rise even further along with our numbers. (Ever notice how many travelers in American airports are now willing to pay more than $2 for a bottle of water that came from spigots in Ireland, France or Brazil?)

It's the price of food -- and that translates right back to the price of water.

An additional 100 million Americans will certainly mean more expensive burgers, say agricultural economists.

It's simple. It takes about 15,000 tons of water to grow one ton of beef -- but only 1,000 tons of water to grow one ton of grain or vegetables.

Even fruit and veggies will be more expensive -- though still far cheaper per calorie than meat -- as water per person grows less.

"It's as expensive as oil -- a big part of our farm budget," farmer Dan Errotaberre said to ABC News in his California orchard.

The water seeping through the drip hoses in his vast almond orchard is meted out drop by drop from shiny aluminum vats and pipes that look more like a futuristic chemical factory than a waterworks -- and a far cry from the water-wasting irrigation ditches that used to flood the San Joaquin Valley farms stretching to the horizon around his trees as far as the eye can see.

In the End, It's Us

America's population does not necessarily have to increase by another 100 million, according to some analysts, even though it is steadily rising for now.

"Maybe we ought to really rethink the population question," Gleick said. "In fact, it's vital."

"A lot of our problems -- not just water and food, but energy production with its global-warming gases, land-use problems with the suburban sprawl, and its removal of farmland and nature -- a lot of our problems would be far easier to solve if we had a smaller population," he said.

Some economists argue that zero or negative population growth, as can be found in Russia and some European countries, is bad for economy.

A growing number of analysts, including Gleick, disagree, arguing that fewer people can make for a better quality of life because of promising new technologies and a growing spirit of of conservation in America.

But, he warns, there's one technology -- often the stuff of pipe dreams -- that will not be a silver bullet.

Seawater NOT the Holy Grail, Just in Case You Were Wondering

Yes, it's true that, just as our bodies are 70 percent water, so is our planet's surface -- 70 percent salty seawater.

But barring a miracle unforeseen by even the most optimistic scientists, some cheap, new technology for desalinization -- taking the salt out of seawater to quench the humanity's growing thirst -- does not seem to be in the offing.

Physicists have been saying for decades that seawater desalinization is a "classic silver bullet fallacy."

It's simple physics, apparently.

The amount of energy needed to strip the sodium (salt) ions away from the water molecules is just too great -- and too expensive -- to make it cost-effective for quenching our thirst or growing food.

And 80 percent of fresh water used by Americans goes to agriculture.

Unless Americans figure out some way to slow --or even reverse --population growth, it seems they must now focus on conserving that most basic medium of life: "Adam's wine" -- water.