Which of the following factors can lead to a decrease in water pH?

The process of recarbonation involves adding carbon dioxide to the water, which subsequently forms carbonic acid when dissolved. This increase in carbonic acid contributes to a decrease in the water's pH level, making the water more acidic. Recarbonation is often used in water treatment processes for balancing pH levels after the removal of hardness or during other treatment processes.

In contrast, adding lime to water serves to raise the pH by introducing calcium hydroxide, which is alkaline. Heating water does not have a significant direct effect on pH levels, and increasing water pressure can affect gas solubility but does not directly lead to a pH decrease. Hence, recarbonation is the process that specifically leads to a decrease in water pH due to the formation of carbonic acid.