With respect to domestic water systems in buildings, what does "stagnant" water refer to?

Stagnant water in domestic water systems refers specifically to water that is not flowing. This condition occurs in plumbing systems when water is left sitting in pipes or fixtures without any movement for an extended period. Stagnation can create a favorable environment for the growth of Legionella bacteria and other harmful microorganisms, as stagnant water often lacks the necessary flow to introduce disinfectants and maintain water quality.

In contrast, treated water indicates that it has undergone processes to eliminate contaminants, which does not directly relate to the flow status. Water with a high pollutant level does not necessarily imply stagnation; it could be that flowing water is contaminated. Regularly cycled water, on the other hand, is kept moving to reduce stagnation and prevent the conditions conducive to bacterial growth. Therefore, the definition of stagnant water is accurately captured by the idea that it is water that is not flowing.