Which of the following is unlikely to occur in a water distribution system?

In a water distribution system, an increase in dissolved gases is indeed the least likely occurrence under normal operational conditions. Water distribution systems are typically designed to function efficiently, maintaining a stable equilibrium of dissolved gases, primarily oxygen and carbon dioxide, which are naturally present in water.

In a well-functioning system, factors like temperature and pressure generally keep the levels of dissolved gases relatively stable. An increase in dissolved gases could potentially occur under certain conditions, such as changes in temperature or pressure, but this is not a routine issue associated with water distribution.

In contrast, decreases in system pressure can happen due to various factors such as high water demand, leaks, or system failures. Failures of water flow can occur as a result of blockages, infrastructure issues, or mechanical failures. Contamination of the water supply can also occur due to cross-connections, aging infrastructure, or external environmental factors. These are common concerns that may arise within a water distribution system, making them more probable than an increase in dissolved gases.