What indicates that both carbonate and non-carbonate compounds are present when total hardness exceeds total alkalinity?

When total hardness exceeds total alkalinity, it suggests the presence of both carbonate and non-carbonate compounds. Carbonate hardness, also referred to as temporary hardness, is primarily caused by the presence of calcium and magnesium bicarbonates, while non-carbonate hardness, or permanent hardness, typically arises from sulfates, chlorides, and nitrates of these minerals.

In a situation where the total hardness surpasses the total alkalinity, it indicates that the amount of calcium and magnesium ions in the water is greater than the bicarbonate levels that can neutralize them. This excess signifies that, in addition to the temporary hardness from carbonates, there are substantial levels of non-carbonate compounds contributing to the overall hardness.

Therefore, the correct choice reflects the dual nature of hardness being measured—both carbonate and non-carbonate hardness are involved, establishing a clear distinction of the water quality being assessed. This concept is crucial in water treatment processes, as it affects the methods utilized to manage hardness before the water is distributed for consumption.