Water is one of the basic 5 elements. Suiton can be used to manipulate water around the user, or to create water from the users chakra. The latter of the toe is more difficult. Water is used to inflict blunt force trauma, and can cause massive internal damage. It doesn't inflict external damage as much as it does internal.
It is strong against fire, because water naturally smothers and puts fire out. It is weak against earth, because earth can be used to dissipate the water, causing it to dissipate, which ultimately makes the water ineffective. It can be used in conjunction with Raiton because water is a natural conductor for electricity, which increases the shock damage. It can also be used with wind, which increases the power of the blunt force of water.
Water is a factor in the following KG- ice, wood, storm, and boil release.
The Hozuki clan has a special form of Suiton that they use to liquefy their entire body, or just certain parts, at will.
Suiton, to me, personifies the calm, yet powerful waves of the ocean. It can be subtly deadly, or forcefully deady, depending on how it is utilized. I find it interesting because it can destroy a person from the inside. While it isn't my favorite element, I find it to be the second most versatile, second only to earth.