Almost every other substance contracts as it solidifies. Ice is about 9% less dense than liquid water — so it floats, lakes freeze from the top down, and life survives the winter underneath. It is also why a frozen pipe splits.

For a molecule this small, water ought to boil somewhere below −70°C. Hydrogen bonding holds it together well enough to keep it liquid all the way to 100°C — which is the only reason there is liquid water on this planet.

Water dissolves more substances than any other liquid, which is how it carries nutrients through every living thing. It is also why it arrives at your plant carrying the hardness, silica, chlorides and everything else it picked up on the way.

Strip everything out of water and it doesn't become gentle — it becomes hungry. Ultrapure water is so eager to dissolve things that it attacks carbon steel and pulls CO₂ straight from the air. In this industry, “clean” and “corrosive” can be the same word.

Almost everything dissolves better in hot water. Calcium carbonate does the opposite — it falls out of solution as temperature rises. That is why scale deposits precisely on the hottest surfaces in the system: boiler tubes and heat exchanger walls, the one place heat transfer matters most. Water saves its worst behavior for your most expensive equipment.

Boiling a kilogram of water takes more than five times the energy it took to heat it from ice-cold to boiling. That enormous latent heat is the entire principle of a cooling tower — evaporate roughly 1% of the circulating water and the rest drops about 10°F — and the reason steam moves more energy than almost any other working fluid.

One liter of water becomes about 1,600 liters of steam at atmospheric pressure. That expansion is what makes steam useful — and what makes a boiler under pressure something you treat with respect.