So much rain - and so little water. South Florida assesses water supply as periodic droughts bring rationing

On the drive here from Miami to discuss south Florida's water outlook with the officials who imposed severe water rationing this summer - and are likely to do so again within a few months - it rained so hard this reporter had to pull off the highway.

A few minutes later the rain stopped and the sun emerged on this peninsular haven for a rapidly growing number of American tourists, retirees, and others.

Such rains can temporarily obscure the concerns raised by periodic water shortages in this area. And officials here want to make wise use of usually abundant water supplies to help south Florida residents through the periodic droughts. After the rains come, a persistent question remains:

Is south Florida running out of water? Moreover, will water shortages curb the rapid population growth of this area (40 percent in southeast Florida during the 1970s)?

The answer, culled from a number of interviews with experts here, appears to be this: No, Florida is not running out of water. But increased demands for it make changes in water use habits of residents necessary and water management a must in order to avoid major disruptions from droughts which occur every 7 to 10 years.

Geologist Abe Kreitman, an official for the south Florida Water Management District (SFWMD) here, says there is enough water to provide for twice the population south Florida now has. ''There's no shortage of water; there's a shortage of management,'' he says.

Mr. Kreitman says that of the roughly 60 inches of rain that falls on south Florida yearly, only about three inches are used by man. The rest either evaporates (20 inches), is used in transpiration - the process by which trees and plants naturally use moisture for growth - (22 inches), or is needed to hold back salt water (7 inches).

The remaining eight inches or so could be used by man, but is not. Most of it flows into the ocean. If only half of that drained portion were used, it could support as many people as now live in southeast Florida and about 3 million additional persons, Kreitman says.

But until this water is better utililzed, south Florida may well have to live with periodic droughts. This summer, with water rationing of up to 25 percent in some areas, the region just ''squeaked'' by a prolonged drought without major consequences, says a water management official here. This year's drought ended with torrential rains from hurricane Dennis in August, which flooded some areas south of Miami but did little to replenish water levels in other areas.

A paucity of rain in recent weeks now makes mandatory water use cutbacks of up to 50 percent in some areas ''a pretty safe bet in future months,'' says Peter Rhoads, director of planning for SFWMD.

Higher water bills are almost a certainty, says SFWMD executive director Jack Maloy. And if the water supply system is made more efficient, demands for water will probably increase, in a ''Catch-22'' dilemma, he says.

Water shortages have become a major issue in many parts of the country, but with its unusual geology and rapid population growth, Florida is particularly sensitive to the issue.

Questions raised here and elsewhere concerning future water supplies include: whether to ration water; whether to try to build expensive new systems to increase supplies; and whether increase water costs to reduce its use.

Put another way: green lawns are nice, but at what price?

In south Florida, where many lawns are equipped with automatic sprinklers, half the domestic use of water is for outside the home: lawns, shrubs, and pools. Lawns are frequently overwatered, studies show. But agriculture uses about two-thirds of the water in this area and officials here say much of that is required because of improper irrigation methods.

Florida is a particularly ''vulnerable'' piece of geography, as one geologist here notes.

Like a flat table, sitting only a few feet above sea level atop a porous bed of limestone, south Florida gets 55 to 60 inches of rain a year. Allowed to stand, this rainfall replenishes underground water supplies, including the giant Biscayne aquifer under coastal southeast Florida. But the semitropical rains also can flood coastal areas. Planner Rhoads recalls his father-in law had to wade through waist-deep water to reach the downtown Fort Lauderdale post office after a flood in 1947.

During the 1950s and 1960s, the US Army Corps of Engineers built a giant plumbing system for the region, a spiderweb network of canals to drain areas normally flooded. Flooding was substantially reduced; new agricultural lands were made available.Today water is drained so quickly to the ocean that underground water supplies and Lake Okeechobee, the main reservoir for south Florida, including Miami, have far less chance to be replenished by rains. When a drought occurs, as it did this year, the problem is compounded.Assessment of the water problem varies. SFWMD board member Nathaniel Reed, an environmentalist and potential guberntorial candidate, says the current system is not adequate to meet future growth. Former SFWMD board member John DeGrove calls this summer's drought ''a shocker,'' and says he feels ''a sense of urgency'' to improve water supplies and management because further cutbacks are likely. ''I think now is the time to strike: people are worried and concerned.''Adds SFWMD geologist Patrick Gleason: ''The drought was a warning.'' But, says SFWMD environmental sciences director Walt Dineen, ''I think there's a little overreaction to the crisis part of it.'' His concern now is that any changes made to increase water supplies might damage sensitive plant and animal life in the Everglades. The best known part of the Everglades is the national park; but several similar undeveloped areas north and east of the park act as giant water conservation areas for the region.''The place has not changed in 500 years; thousands of wading birds use it,'' says Dineen. A proposal to pump back some of the water now drained to the ocean by canals has him concerned that agricultural and other pollutants in the pumped water may harm the ecology of the area. His concern is shared by John C. Jones, executive director of the Florida Wildlife Federation. Mr. Jones also says the water supply of cities should be limited by the SFWMD in order to control population growth.The option of curtailing growth due to water shortages in drought periods is ''not an option,'' in the opinion of Jeanne Bellamy, a Miami banker and SFWMD board member. Even though some local governments would like to use water shortages as an excuse for limiting growth, she thinks anyone who wants to move here should be allowed to do so.The so-called ''backpumping'' proposal is the only major physical change in the regions plumbing system being given serious consideration at this time, says SFWMD director Maloy. Except for that proposal, he says, ''I think we're at the point where we've spent as much public money as ought to be spent. We've got to learn to live with the system.''So how can this region supply all the water for showers, lawns, businesses, and farms if the rapid growth of the past decade continues?SFWMD officials' average projections estimate the population of southeast Florida will increase by 57 percent between 1980 and 2000, increasing the demands for water by some 45 percent. But there is ''considerable uncertainty'' about such projections, says planner Rhoads. Florida's population growth depends on such unpredictable things as the cost of home heating fuel in northern states, he says.Most regional and local water management officials are expressing little sense of urgency. For example, city council members of one coastal town relaxed when informed by regional experts that saltwater would not intrude into the town's drinking water for two years (Saltwater is held back from coastal freshwater wells by the freshwater itself, but can intrude when freshwater supplies fall).Most SFWMD officials express confidence that there is enough water to meet any demands till the year 2000. Public cooperation in complying with mandatory water cutbacks this year was good - the cutbacks exceeded the targets. Public reaction was mild.'I felt a little guilty when I took a shower,'' says one Miami woman. Miami Mayor Maurice Ferre says the regional water officials know what they are doing and handled the shortage well.Helping to offset future demands from urban residents is a likely decline in agriculture in the area, says Jeanne Bellamy. The black muck exposed by draining and valued as farm land is drying out and will reduce farming by the year 2000, thus cutting back on the major use of water, she says.Desalinization, by one of several processes, is another way of boosting water supplies, if necessary, officials say. But this is an expensive method. Key West relies heavily on desalinized water and pays close to $10 per 1,000 gallons for it, compared with an average of about $1.30 in Dade County (which includes Miami). But the cost of desalinizing brackish water would be only two to three times higher than normal rates.Officials here are also considering allowing water to stand on recharge areas longer, at higher levels, to better replenish underground supplies.