OK it’s not an ocean, it’s groundwater trapped in cracks and pores under the Martian surface. And unfortunately, it’s way too deep to tap. The ground water is enough to cover the entire surface of Mars with an ocean to the depth of about a mile! But the water is about 10 miles underground. That would be impossible to tap here on earth, much less on Mars. There’s probably all kinds of little alien microbes swimming around down there.

Scientists find oceans of water on Mars