Which chemical is known to decrease corrosion rates in water systems?

Calcium Carbonate (CaCO3) plays a crucial role in decreasing corrosion rates within water systems due to its ability to increase water alkalinity and pH levels. When calcium carbonate is present in water, it helps to stabilize the water's chemistry by forming a protective layer on the interior surfaces of pipes and equipment. This layer can effectively inhibit the leaching of metals, such as lead and copper, from the plumbing system into the drinking water. Additionally, by increasing the hardness of the water, calcium carbonate can reduce solubility and therefore the mobility of corrosive elements.

The other options do not have the same effect on corrosion control as calcium carbonate. Sodium chloride, for example, does not contribute to the alkalinity or hardness in a way that reduces corrosive properties. Magnesium sulfate, while beneficial for certain nutrient levels in water, does not provide the same corrosion-inhibiting benefits. Potassium nitrate is primarily used as a fertilizer and, like the others, does not build protective measures against corrosion in piping systems. Therefore, calcium carbonate stands out for its specific role in reducing corrosion rates in water systems, making it the preferred choice in this context.