Water is as ubiquitous in SimCity 4 as it is in the real world, and may refer to several different "types" of water.
Natural Bodies of Water
Like the real world, SimCity 4 terrain can consist of either land or water. Unlike the real world, all natural water in the game exists at sea level. Ships and ferries can travel in natural water, and bridges can be built over natural water. Certain lots, such as ferry terminals, marinas, and some seaports can be built partially over water. Natural water can reflect water pollution by turning black.
Ploppable water is a category of mods that allow you to place surface water in the game.
Water is one of the main utilities that a lot will need in order to grow. It can be supplied by a water pump or water tower and transported by using water pipes. If there is no water supplied to a building that requires it, it will display the water zot. Dirty industries can pollute the water, which degrades water pump performance, and eventually stops the water pumps and towers from functioning. This can be counteracted by placing water treatment plants in your cities, or locating water pumps and towers away from polluting industries.