What compound could be used to increase alkalinity in water?

Calcium carbonate (CaCO3) is commonly used to increase the alkalinity of water due to its ability to dissociate and release carbonate and bicarbonate ions when dissolved. These ions can help buffer the pH of water, effectively increasing its alkalinity. Alkalinity is crucial for maintaining stable pH levels in water systems, as it plays a significant role in preventing sudden changes in acidity which can be harmful to aquatic life and the efficacy of water treatment processes.

In contrast, the other compounds mentioned do not have the same direct effect on alkalinity. Sodium chloride primarily serves as a source of sodium and chloride ions without contributing to alkalinity. Potassium nitrate, though a source of nutrient potassium and nitrogen, does not influence water's buffering capacity. Magnesium sulfate is primarily used for adding magnesium and sulfate ions, and while it can have a role in water chemistry, it does not contribute substantially to increasing alkalinity.