SAN DIEGO -- A San Diego couple said they have an invention that could help solve the state's water woes and end world hunger, 10News reported.

Phyllis and Collie Davis' Bay Ho back yard has a unique garden that has no soil. It has a little peat moss, and the only water required is in the heated tank that houses a secret ingredient -- white fish tilapia.

The feces of the well-fed fish are sent into a pumping system that isolates the good nutrients. That nutrient-rich water is then pumped through the gravel bed several times a day. Seedlings with a bit of peat moss are rooted in the gravel.

Phyllis Davis told 10News, "It fills it up and gives it all it needs to grow tall, healthy and fast."

The Davis' mini-farm is a four-decade-old hobby that turned into a labor of love for the couple.

The mini-farm can produce a big harvest, the couple said. The enclosed 50 sq. ft. plot can produce 500 vegetables and 200 pounds of fish in a year -- which can help feed a family of four for a year and comes with a miniscule water bill.

The couple said their invention uses 95 percent less water than a farm growing the same amount of food.

"That's because you continually reuse the water. It doesn't go back into the soil, doesn't evaporate. We believe this is a game changer," said Collie Davis.

The system's energy costs are also low. At any given time, the system can typically run on the equivalent of a 60-watt light bulb.

The couple said the cost of their farm can range from $8,000 to $200,000 for the biggest farms, with the product paying for itself within a year.

They said they've been contacted by people, schools and prisons in 172 different countries about their invention.

For more information on the Davis' system, go to www.portablefarms.com.