Mine just grows in a pond. The stems float and produce lots of roots at the leaf nodes. It's very easy and seems to get enough nutrients from the fish in there.

Get a bunch from the Asian market. Any cuttings from that will quickly sprout roots. The Vietnamese markets should have them. Some of my neighbors grow them in baby pools filled with dirt. They grow fast!

I’ve been growing kang kong in my backyard here in LA, zone 10, and it’s actually pretty straightforward. I started from seeds I ordered online since it was hard to find around, and they sprouted in about a week. It likes a lot of water and warm, sunny spots, so I keep the soil moist most of the time. If you can’t find plants locally, sometimes Asian markets or local plant swaps have cuttings. Just make sure it doesn’t dry out and it usually grows fast.