What type of water is least likely to cause scaling in a boiler?

Deionized water is least likely to cause scaling in a boiler because it has had most of its mineral ions removed, such as calcium, magnesium, iron, and others that contribute to scale formation. In boilers, scale can seriously impact efficiency by forming deposits on heat transfer surfaces, which can reduce heat transfer and increase energy costs.

By contrast, municipal water often contains various minerals and contaminants that can foster scaling. Groundwater typically has a higher concentration of minerals, particularly calcium and magnesium, both of which are notorious for causing boiler scaling. Distilled water, while also low in minerals, might still carry trace amounts or other impurities depending on the distillation process, making deionized water the superior choice for preventing scaling.