Three years ago Marshall Rose was unemployed, a college dropout and Vietnam veteran unsure about his future.

Today Rose is president of J.K.W. 5000 Ltd., a three-year-old California firm specializing in water-saving devices for the home. And with the worst drought in recent history still ongoing in California, business is booming. Conservation, sometimes enforced by rationing, has made the 30-year-old businessman a success story, the proud owner of a modern $160,000 suburban home with a sparkling, new $20,000-plus Porsche Carrera sports car in the garage.

The Western drought, now in its third year, has bankrupted some farmers and inconvenienced millions of consumers. But it has also caused a boom in industries ranging from well drilling to firefighting supplies.

The well drillers, in particular, have been much in demand. Their tapping of underground pools has kept many farmers solvent.

"The majority of well drillers have doubled or tripled their drilling crews this year," said Don Mickel, executive director of the Associated Drilling Contactors of California. Some drillers have been booked three ton six months at a time."

Nearly 14,000 wells were drilled in California in the fiscal year that ended June 30, according to the State Department of Water Resources - a 50 per cent increase over the previous year. Mickel estimates these wells brought more than $500 million in revenues to drillers across the state.

"This has been our biggest year in history," says Jim Bowman, manager of Bakersfield Pump Co., in the heart of the drought-stricken San Joaquin Valley. "We've had guys working out there 14 hours a day, seven days a week."

Some drilling industry experts predict a prolonged room. "People are busy praying for rain, but it will take six to seven years of deluge to end this drought," said Mickel.

The drought may also be a blessing for companies that sell water-saving "drip" irrigation systems. Larry Gargan, general manager of Bakersfield's Irrigation Supply Co. says many farmers are now attracted to the "drip method," first developed by desert farmers in Israel, because it can save between a third and a half more water than conventional irrigation systems.

"It's still in the development stage," Gargan said. "But now there are many farmers out there using other methods who have expressed an increased interest in 'drip'. That has never happened before. It's been a very good year for us. We can't complain from a business standpoint, that's for sure."

While the drought has caused severe problems in the San Joaquin Valley, usually the richest agricultural area, farmers in some other regions have been faring much better.

A group of farmers on the Sacramento River was able earlier this year to sell their water to desperate San Joaquin agriculturalists several hundred miles to the south for over $1 million, in a deal arranged by the federal Bureau of Reclamation.

Dick Willey, head of the six-farmer group that sold the water, said they had to forgo planting a total of 2,500 acres of rice in order to make the deal. "This was a question of survival for those people," Willey explained. "And from a personal point of view, let's just say it worked out satisfactorily for us."

Another group that has weathered the drought well is the firefighting chemicals and equipment industry. The dry summer was one of th worst fire seasons on record. And if the hot Santa Ana desert winds start blowing in southern California, some fire experts believe, there could be another rash of blazes before Christmas.

"I've been in this business 31 years and this is the best year ever," said Clyde Stratton, general manager of Wiloc Fire Equipment of Portland, Ore., a major supplier of fire hoses and tools throughout the West Straton said his company, a subsidiary of Canada-based Wajax Ltd., experienced a 100 per cent increase in business this summer over last year.

"We did a real good volume, especially July and August, really good," Straton said. "There were a lot of fires and people are getting pretty nervous so they've ordered a lot of equipment."

The link between fire danger and drought is evident in the sudden popularity of the chemical fire retardant Phos-chek, manufactured in Ontario, Calif., for Monsanto Corp.

Phos-chek, according to manager Don Peterson, makes water molecules soak into substances better. "Phoschek makes water wetter," Peterson said, and in many cases this summer it helped firemen "stretch" limited water supplies.

At one time this summer the Phoschek plant in Ontario was on a 24-hour, seven day schedule. Now output has returned more to normal, but Monsanto has doubled the stockpile of Phos-chek in its warehouse, Peterson said, in case the drought leads to another severe fire season.