What does old still water smell like?

Old still water often has a musty or earthy smell due to the presence of organic matter, algae, and bacteria that can thrive in stagnant conditions. This odor can be reminiscent of damp soil or decaying leaves. Additionally, if the water is contaminated, it may emit a stronger, unpleasant odor from pollutants or chemicals. Overall, the scent is usually a sign of stagnation and lack of aeration.