Reagent water can be prepared by which methods?

• A. Adding salt to water
• B. Heating water only
• C. Filtering only
• D. Distillation, deionization, adsorption, reverse osmosis or a combination thereof

Answer: (D)

Reagent water must be highly purified, meaning dissolved ions, organic contaminants, and particulates are reduced to very low levels. The ways to achieve that are methods that actually remove dissolved substances, not just alter temperature or physical form.

Distillation works by boiling water and condensing the vapor, which leaves most dissolved minerals and salts behind in the original vessel. It also helps remove many organic compounds and pathogens, producing very pure water. Deionization uses ion-exchange resins to swap ions in the water for hydrogen and hydroxide ions, effectively removing dissolved ionic species and producing water with extremely low conductivity. Adsorption, such as with activated carbon or other adsorbents, captures organic molecules and some volatile contaminants, cleaning the water of organics and certain impurities. Reverse osmosis pushes water through a semipermeable membrane, which blocks ions, many organic molecules, and larger contaminants, providing a broad purification step. Using these methods singly or in combination—distillation alone or with other steps, deionization alone or after RO or distillation, adsorption as a polishing step, or RO followed by deionization—can yield reagent-grade water.

In contrast, adding salt to water clearly adds impurities; heating only does not remove dissolved salts or organics from solution and can even concentrate non-volatile substances. Filtering only removes particles but leaves dissolved ions and most dissolved contaminants behind.