A clue to the wise: Wear something that won't be ruined by water, keep your wallet and cellphones in plastic bags, and be prepared for people dousing you with water and smearing a water/powder mixture on your face! They even douse cops and soldiers:
(Weapons-related content: The Thai Royal Guard carries a Thai-built licensed version of the HK in 223, with 40 round mags.
I got absolutely soaked, and loved it. SuperSoakers abound. I intend to get one today, so I can fight back.
It's also a Buddhist religious festival. My g/f, the Sergeant Major, declared that we were going to go to the Wat (temple). I was thinking singular. One.
NOPE: She meant Wat, plural. As in NINE of them. As I respect her beliefs I accompanied her while she paid her respects. I do not enter the Wat, but do enjoy the artwork, sculpture, and talking to the occasional monk who wants to try out his English.
Here's a link to a couple pages of pix to give you some idea of how crazy it gets: Songkran Water Festival
Edited for pix and to update title