In California’s Central Valley, water prices have risen as high as $2,000 an acre-foot. As a price comparison, in non-drought times water can sell for as low as $250 per acre-foot. On the highest end, other farmers have sold their future water rights for as high as $5,000 per acre-foot. Two of the biggest players in the California’s water scene are Stewart and Lynda Resnick. They’re the billionaire owners of The Wonderful Company, known for their pistachios, mandarin oranges, and POM wonderful pomegranate juice. The Resnicks are also majority owners in the Kern Water Bank, one of California's largest underground water storage facilities. A water bank is an area mostly underground where water can be stored reliably until it is needed. From above water banks tend to look like puddles, but underneath they can hold hundreds of thousands of gallons. For more than three decades Forbes reporters have tracked the fortunes of the richest people on the planet: putting dollar figures to their business empires, their one-of-a-kind art, their private islands and more. Now, in a new series called “Priceless,” we’re taking you behind the scenes to show you how we determine the value of the most unique assets owned by members of The Forbes 400. Read the full story on Forbes: Subscribe to FORBES: null Stay Connected Forbes newsletters: https://newsletters.editorial.forbes.com/ Forbes on Facebook: http://fb.com/forbes Forbes Video on Twitter: http://www.twitter.com/forbes Forbes Video on Instagram: http://instagram.com/forbes More From Forbes: http://forbes.com/ Forbes covers the intersection of entrepreneurship, wealth, technology, business and lifestyle with a focus on people and success.