Kelly Krolicki, age 8, of Portland, Me., for her question:

WHO INVENTED INSIDE PLUMBING?

Plumbing in our modern houses represents many years of inventions. Kitchen and bathroom fixtures are the last stages of a long line of valves, pipes, pumps, boilers, reservoirs and water-treatment plants. No one person or era can be credited with the modern miracles that give us clean, safe hot and cold water whenever we need it. Indoor plumbing was not "invented." It evolved over the centuries as man's needs became more sophisticated and cities became more complex.

The most important developments to influence modern plumbing were made some 3,000 years ago by the Greeks and the Romans. They supplied large quantities of water to their cities and towns by means of a large channel or pipe called an aqueduct. Water flowed from rivers, or melted snow, down to its desired location by gravity.

The water was distributed to buildings and community centers by lead pipes. Today lead is no longer used because small amounts of lead may dissolve in the water, and even minute quantities of lead can be dangerous to health. Modern pipe is usually copper, cast iron or plastic.

With the decline of the Roman Empire by the 5th century A.D., the advanced water systems were abandoned. A thousand years later London reconstructed much of the piping system built by the Romans, even using Roman plans in the process.

The invention of the steam engine in the late 1800s paved the way for modern plumbing to enter our homes. With the steam engine, water could be pumped through pipes to any place it was needed. Before this, man depended on the pull of gravity to control the water's flow.

The first plumbing fixture in the United States was the kitchen sink, which meant cooking and cleaning up could be done without hauling in water from outside. Then came the bathtub, a square boxlike affair made of wood and lined with lead, tin or copper. In 1871 a patent was granted for a water closet. This was not the "first" modern toilet by any means, however--in the late 1500s an Englishman, Sir John Harrington, proposed one, and 200 years later a London watchmaker patented a toilet with a trap.

Water is indispensable to man. Early peoples settled close to rivers or lakes so that fresh water was never far away. Until the 20th century, people relied primarily on wells or cisterns for their water. Today our homes are supplied by water distributed through underground pipes. It is cleaned by filtering and then treated with chemicals to purify it.