What would be a good topic to write a chemistry research paper on the subject of water?
One very good water topic, in which chemistry is essential, is the Water Cycle in nature. Because most of the organic life on Earth depends on water in some form, the water cycle is vital in all areas of science.
Water cycle describes the movement of water -- H2O -- through the various phases of matter, mostly liquid and gas. Almost 97% of the planet's total water mass is in the oceans, where it remains largely in saline-liquid form; only about 2.5% of the planet's water is fresh, or saline-free. During the normal course of a day, water from the oceans evaporates into the atmosphere, in a gaseous form, where it is part of the atmospheric cycle -- evaporated water is always saline-free. When it is able to collect together in clouds, it precipitates, forming either a liquid or solid form -- rain or snow. This precipitation is heavier than air, and so falls to return to the liquid in oceans, lakes, and groundwater, or becomes part of the icecaps at the poles, where it remains in solid form.
The chemical reactions of the various phases of water to the atmosphere and surrounding environment are integral to the water cycle itself; for example, icebergs forming in ocean water are always saline-free, because they cannot form a solid ice structure, even at below-freezing temperatures, with saline attached to the water molecules. Icebergs calved from glaciers are also saline-free because they are mostly formed from precipitation, which comes from evaporated saline-free water.