Which statement is inaccurate concerning the disadvantages of soda ash treatment?

The statement that soda ash treatment adds hardness to the water is inaccurate. Soda ash, or sodium carbonate, is primarily used to soften water by reducing the level of temporary hardness caused by calcium and magnesium bicarbonates. When soda ash is added to water, it reacts with these hardness-causing minerals, precipitating them out of the solution, which effectively decreases the hardness of the water.

In contrast, the other statements reflect true aspects regarding soda ash treatment. Although it can have a significant initial cost due to the materials and equipment needed, and it may require additional filtration methods like sand filters to remove precipitated particles, these issues relate to practical operational considerations rather than the fundamental chemical nature or function of soda ash in water treatment. Furthermore, while soda ash can be used in some residential applications, it is indeed more commonly applied in industrial settings, addressing the specific requirements of those sectors.