NO wonder they are called conveniences. Flush toilets swirl human waste down the drain quickly and neatly. But the convenience comes with a rising price for all that follows the flush — a cost that is often paid by municipal water and sewage treatment systems.

Now some groups are rethinking the venerable technology of the flush toilet, particularly for regions that lack such systems or for places where waste water treatment plants, many of them aging, are overburdened by the demands of fast-growing populations.

The Bill and Melinda Gates Foundation has begun a “Reinvent the Toilet” competition and awarded $3 million to researchers at eight universities, challenging them to use recent technology to create models that needn’t be connected to sewers, or to water and electricity lines, and that cost less than pennies per person a day to use. Later prizes will include financing for one or more winning prototypes to be tested and produced commercially.

“The present toilet is a 19th-century device that does not meet the needs of a vast part of the world’s population,” said Frank Rijsberman, an executive at the foundation. Instead, he said, about 2.6 billion people without access to sewer-linked systems must use simple latrines, holes in the ground or just the nearest available spot — a situation that can lead to many health problems, like acute childhood diarrhea.