A Skywater 300 atmospheric water generator, naturally.  In her own words, 

This property was a dust bowl when I bought it,” Kerr says, “and now it’s so green. Obviously I’m aware of the drought problem in California. This (Skywater 300) system really just pulls water out of the sky. It was a very thoughtful present because (Evan Spiegel) knows how much I love a garden.
— Miranda Kerr

See the excerpt below, or read the full article at Harper's Bazaar (click here).

 Miranda Kerr's Skywater 300 unit keeps the water flowing, all while helping fight the drought facing California

Miranda Kerr's Skywater 300 unit keeps the water flowing, all while helping fight the drought facing California

Kerr, who launched the organic skin-care line Kora Organics in 2009, is committed to a healthy, sustainable lifestyle, and her home reflects that. Her fridge is stocked with fresh produce, and she’s an avid cook who entertains frequently. (Her favorite meal? Slow-roasted organic chicken and a big salad.) The hillside behind the house is terraced with garden beds, where Kerr grows her own kale, and Flynn helps her pick strawberries, blueberries, and lemons. ... But the most impressive enviro upgrade was a gift from Spiegel, a machine made by Island Sky called the Skywater 300, which draws moisture from the humidity in the air and produces enough water for the entire house, including showers, drinking water, irrigation, and a waterfall that cascades into a koi pond.

”This property was a dust bowl when I bought it,” Kerr says, “and now it’s so green. Obviously I’m aware of the drought problem in California. This system really just pulls water out of the sky. It was a very thoughtful present because he knows how much I love a garden.”