Nowadays Thais will walk the streets having 'water fights' using containers of water or water guns, or stand at the side of roads with a hose and soak any one who passes by.
You may also get covered in chalk, a custom originating from the chalk used by monks to mark blessings. This combination of water and powder is almost identical to the celebrations of Holi, and indeed, it maybe that the customs originated in India as certainly Songkran is celebrated more widely and longer in the Northern part of Thailand.
Even more interesting is that the custom of water fights pops up in a distant place at the same time of year. Dyngus Day is celebrated on Easter Monday in Poland, and on the Monday the custom is that boys get to soak girls with water, but on the Tuesday, the girls get to throw crockery at the boys - again the water and powder combination.
As mentioned, Songkran is a Cleaning Day, both physically and spiritually. On the physical side, in addition to cleaning other customs are that anything old and useless must be thrown away or else it will bring bad luck to the owner. On the spiritual side, some people make New Year resolutions.
The Thai people celebrate this festival with water. Everyone gets soaking wet and since it is the hottest season of the year, the custom is quite refreshing. Songkran is a Public Spring Cleaning Day, supported by the religious belief that anything old and useless must be thrown away or it will bring bad luck to the owner.
During the afternoon of the 13th, Buddha images are bathed as part of the ceremony. Young people pour scented water into the hands of elders and parents as a mark of respect while seeking the blessing of the older people. In ancient days, old people were actually given a bath and clothed in new apparel presented by the young folks as a token of respect for the New Year.