Barbara, Spence., age 12, of Lansing, Mich., for her question:

Will our water supply ever run out?

'We are not surprised to hear that a showery day has given us an inch of rainfall. But if the weatherman reported that Michigan had been doused with q¬billion tons of fresh water, we would suspect a major disaster. However., this is roughly the weight of .one inch of rainfall over the entire state of Michigan. It is enough to supply the drinking water for the world's human population for several weeks,

Experts are seeking a cheap way to take fresh water from the salty sea, because the world, they say, faces a critical water shortage. Our present supplies come from rain and snow, and every year the clouds shed enough fresh water to cover the entire globe to a depth of 32 inches. This annual gift will continue as the sun dries up moisture from the seas and distributes it all over the world.

Onto one acre, an inch of rainfall sheds 113 tons or roughly 30,000 gallons of water. A person can manage with maybe less than a gallon of drinking water a day. But to live comfortably, we need water for cooking and washing. A healthy sewage system uses 25 to 50 gallons of water for every gallon of water we drink. A county water system usually allows us 150 gallons apiece for our daily needs.

What’s more, the rain does not fall neatly into our storage reservoirs, and most of the bounteous supply escapes us. Two thirds of the world's rain falls into the sea, A quarter of the land rainfall runs into rivers and also joins the sea. Some evaporates and thirsty plants and animals take an enormous quota from the world's fresh water. In the growing season, one acre of corn soaks up 15 inches or 450,000 Gallons of rain and melted snow from the soil.

Floods of streaming water are used by industry. It takes 270 tons of water to make one ton of steel, and 1400 tons of water are used to make a ton of rayon. We live in an age of expanding industry, and the need for water and more water increases year by year. The human population is also increasing, and its needs must be met with more sewage and water systems. The growing human family must be fed, and this requires more irrigation to provide the water for extra crops, It is true that our planet is doused with an abundance of water, but we must plan and work hard to make sure that enough of this water is on hand to meet our needs now and in the future.

Someday soon we hope to learn that the experts have found a profitable way to process fresh water from the sea. This water could supply cities and be piped inland to irrigate the wastelands. The seas cover more than 11,.5 million square miles to an average depth of two and a quarter miles. A square mile of water one inch deep 'weighs about 72,300 tons, and a gallon of water weighs roughly eight and a half pounds. You can use these figures to estimate the amount of water we might possibly take from the oceans.