However, with modest water-conservation efforts and an emphasis on more compact development, the state could reduce the projected water demand and keep more farmland in use, the report by 1000 Friends of Florida, the state Department of Agriculture and Consumer Services and the University of Florida showed.
But the alternative approach, limiting water use and development, may not be enough in areas of the state that are already experiencing water shortages, the report warned.
"Water is Florida's golden goose, and we must ensure that we have a reliable, abundant and clean supply of water now and for future generations," Florida Agriculture Commissioner Adam Putnam said. "A long-term and strategic approach is crucial to protecting the quality and quantity of our most precious resource."
Putnam said the state made some improvements with the passage of legislation this year calling for more water planning and the development of water resources, "but more work remains to be done."
Working from a 2010 baseline, the "Water 2070" report shows the state uses about 5.27 billion gallons per day, with a projected rise to 8.1 billion gallons per day if current practices continue and if the state's population, which is more than 20 million now, expands by 75 percent.
Water usage related to development is projected to more than double to 6.48 gallons per day in 2070, while agriculture water usage would decline by 24 percent due to the conversion of farmland to homes, shopping centers and other development.
Under that trend, a third of the state would be developed, with the conversion of 5 million acres, including 2 million acres of agricultural and natural lands, to development, the report said.
However, with better water conservation efforts, representing a 20 percent decrease in per-capita usage, as well as an emphasis on more compact development, the water demand in 2070 could be trimmed to 6.85 billion gallons per day, or an increase of 30 percent over 2010.
The report said efforts by the government and individuals will be necessary to curb water usage while accommodating population growth, with a major emphasis on encouraging homeowners and others to reduce landscape watering.
"The single most effective strategy to reduce water demand in Florida is to significantly reduce the amount of water used for landscape irrigation," the report said.
Among the recommendations to reduce irrigation demand would be the use of "Florida friendly" landscaping, soil moisture sensors and fewer automated sprinkling systems, which use more water than manual watering, the report said.
Another area for water conservation would be the increased use of reclaimed water, said the report, which also labeled the use of desalinization, the conversion of sea water to fresh water, as too costly and ineffective to meet Florida's future water needs.
Ray Smart, president of 1000 Friends of Florida, a nonprofit environmental group that helped write the report, said private citizens and the government can make a "significant difference" in improving water conservation.
"Outdoor irrigation is the major contributor to development-related demand, and steps to reduce the amount of water lost through irrigation would go a long way to make Florida's future more sustainable," Smart said.
But the report also said more aggressive efforts in conservation and development reforms may be needed in areas of the state where the water supply is already stressed.
Peggy Carr, a professor at the University of Florida Geoplan Center, which also worked on the report, said there is "enormous variability in the existing and projected water demand across the state, largely due to population variation."
Carr used the example of Central Florida, which includes the Orlando area as well as Tampa Bay, with the report projecting a 7.5 million increase in residents in that area by 2070.
"The water shortfalls in that region are likely to be particularly acute," Carr said. "Maintaining adequate flow for springs, wetlands and rivers will become increasingly difficult."
An additional 15 million Florida residents by 2070 could increase the demand for water by more than 50 percent, with a third of the state being paved over and a noticeable decline in agricultural land, according to a new report.