Songkran is actually Thai new year which falls on 13th April and goes on till 17th April every year. The fact is that Songkran ends on 15th April however in Pattaya it is extended till 17th April, just to get more wet.
Songkran is celebrated by Thai people by visiting Buddhist Temples and offering food to monks. It is followed by poring water over Buddhist statues also called as Abhisheka from the Hindu traditions. This is a form of purification or a method of cleansing ones from all the sins and doing this on a new year is believed to me more auspicious.
Hindu/ Indian Connection
The word "Songkran" comes from the Sanskrit word saṃkrānti literally "astrological passage", meaning transformation or change. This term is actually borrowed from a south Indian Hindu festival called "Makar Sankranti" which marks the arrival of spring season. Songkran, however, was traditionally computed according to the method described in Suriyayart, the Thai version of Hindu Scripture Surya Siddhanta. The celebration starts when the sun enters Aries according to the sidereal zodiac system same as Makar Sankranti.
The New Year is now officially celebrated on January 1st, Songkran was the official New Year until 1888, when it was switched to a fixed date of 1 April. Then in 1940, this date was shifted to 1 January however the traditional Thai New Year Songkran was transformed into a national holiday and it is still followed across Thailand. In 1989, the Thai cabinet fixed Songkran at 12–14 April, despite the correct starting date (13 April at 20:57).
According to thai people, Songkran originated from the birth of Kapila Brahma or Phra Phrom however there are many conflicting stories for this.
The Songkran is known for its water festival. Major streets are closed to traffic, and are used as arenas for water fights. Young or old, everyone participate in this tradition by splashing water on each other and spreading joy.
How to greet in Thai
Happy Songkran's day - Suk-San-Wan-song-Kran (สุขสันต์วันสงกรานต์)
Happy New Year - Sa-was-dee-wan-pee-mai Khrap/kha (สวัสดีวันปีใหม่ ครับ/ค่ะ)