Our planet has roughly 1,400 million cubic kilometers of water — no more and no less.

It's a fixed commodity. The same molecules that once slaked the thirst of dinosaurs are the same molecules that flush our toilets. And those toilets are running dry.

Americans use, on average, 13 million gallons of water every minute — 14 times faster than the natural rate of replenishment.

For this very reason, the Government Accountability Office released a report last October stating that by the year 2013, some 36 states will be facing serious water shortages.

Many high-minded ideas have been proposed to solve this coming crisis, but the simplest solution may come down to plumbing.

There are 300 million toilets in the U.S., and they are the biggest water wasters we have. Many use three to five gallons with every flush.

To combat this excess, Congress in 1992 passed the Energy Policy Act, mandating that all new toilets installed in America be of the low-flow variety, which use a seemingly miserly 1.6 gallons per flush (gpf).

Unfortunately, the poor quality of those original low-flow designs often forced users into multiple flushes and created a toilet-smuggling industry across the Canadian border.

That was many years ago. The plumbing industry says things have improved quite a bit since then, but the question remains: Do any of these new-fangled chamber pots really help the environment?

In 1999, looking for a way to drive more traffic to his Web site (www.terrylove.com), Seattle-based plumber Terry Love began installing low-flow toilets in his own home and those of close friends and relatives.

He became a one-man consumer report and the only field researcher currently working with real poop (everyone else uses soy paste) and real toilet paper (go figure).

"For 1.6 gpf, most American manufacturers simply made the tank smaller," Love said. "But at 1.6 you have to redesign the trapway (a portion of piping hidden beneath the toilet) — that's why those toilets didn't work well."

The low-flow cause was instead taken up by companies in parts of the world where drought is a much more common problem.

Almost 15 years ago, the Japanese manufacturer Toto came up with what many still consider the best solution, its G-Max design.

Toto used a novel clay-drying process and computer-modeled hydrodynamics for greater accuracy in bowl design, and a patented S-shaped trapway that increases disposal velocity.

These two developments solved the older models' problems. Today, according to Love, "nearly every top-of-the-line model on the market is a Toto rip-off."

These second-generation low-flow toilets now save Americans $11.3 million dollars per day on their water bills, though it's still not enough for some people.

"1.6 gallons may be the law of the land," said Val Little, Director of the Water Conservation Alliance of Southern Arizona, "but around here that's old hat. We're now moving to high-efficiency toilets (HET)."

HETs use at least 20 percent less water than the low-flow variety. There are standard 1.28 gpf gravity-assisted models that rely on better bowl design to do the job, and pressure-assisted models that flush around 1.1 gpf and use a blast of air (air is the pressure-assist) to move matter.

Some utilize a jet of water to shred toilet paper; others have a dual-flush system that offers 0.9 gpf for clearing liquids and 1.6 gpf for heavier loads.

The EPA has also gotten behind the HET movement, creating a "WaterSense" label to vouchsafe choice products.

"WaterSense is a lot like the EPA's EnergyStar label," EPA Assistant Administrator for Water Ben Grumbles said. "It signifies that a toilet flushes at less than 1.28 gpf and performs as well, if not better, than its competitors."

So far over 10 companies and 100 products have received the WaterSense designation (a full list is available at www.epa.gov/watersense), but some of those products may not be quite what the government claims.

The EPA has signed off on Vortens toilets, but Love found that their 1.1 gpf pressure-assisted model moves too little water to prevent bowl stains and — even worse for a water-saving toilet — often leaks.

These are only some of the concerns.

Currently, no one makes toilets out of eco-friendly materials. Plastic parts can only become landfill. Porcelain doesn't decompose at all.

In the early '90s, at the time of the Energy Policy Act, the best disposal idea was to turn old toilets into artificial reefs.

Unfortunately, ocean currents bashed the bowls to pieces. Porcelain shards killed the fish, and the Department of Fish and Game killed the program.

These days, we pulverize the porcelain and mix the remains with asphalt for roads — a process that still eats up considerable energy, but is better than any known alternative.

Still, since older toilets currently waste five billion gallons a year, these issues are not enough to offset the potential good of low-flow toilets and HETs. Even better, as things begin to change, much of that saved water will become saved money.

"These new HET designs will save consumers [each] about $90 annually on their water bill," Grumbles said.

It may not sound like much, but since the average toilet lasts more than 20 years, that's about $2,000 total per throne.