Name and location in Chinese: 澄迈老城古驿站瀑布 (Chéngmài Lǎochéng Gǔyìzhàn pùbù).
A while ago I saw some good photos of a waterfall in Chengmai county on the Chinese internet. I happened to be in the area and so decided to see the waterfall in real-life. Most of northern Hainan is flat so waterfalls are scarce.
The waterfall is on the edge of Laocheng Town, which is about 25km west of central Haikou. There is a small river that runs through the town and out to sea. As is common in Hainan, there are few signs to minor attractions like this waterfall, so it is a little hard to find. Furthermore there isn't even a path. A mud track from the road leads most of the way. The waterfall is about 10 metres high and 50 metres wide.