I had the privilege (happy accident) of being in Chiang Mai, Thailand during their Songkran festival - Thai New year. For almost a week, the streets were flooded with people AND water. Everyone loads up in the back of trucks, tut tuts, taxis, they line up on the sides of roads and roof tops, All for one massive water fight. Like, this is a country-wide water fight of epic proportions! They will use any and everything to soak each other. Water guns, garden hoses, fire hoses, buckets, trash cans, anything that can hold water was a weapon.
Now, I know very little about this festival and the meaning behind it, but from my light reading, the water fight is supposed to have some symbol of washing away each others sins.