For those of you seeking even more info, here are two snippets of news.
The first concerns a travelfish entry on Phu Quoc, Vietnam Tranh stream, possibly the only (seasonal) waterfall on this otherwise dry island.
The other concerns a saltwater waterfall in Trang province, Thailand. Posted on the TTR Weekly it mentions that money will be thrown into creating visitor facilities for this rare waterfall.
'The downside is that the waterfall is only visible during the 14th to 15th full moon and first and second days of the waning moon from 0600 to 0800 and from 1700 to 1800'.
Hmmm, ....