Which of the following is an indication of water hardness in a plumbing system?

The build-up of scale in appliances is a well-recognized indicator of water hardness in a plumbing system. Hard water contains high levels of calcium and magnesium ions, which can precipitate and form deposits when water is heated or when it evaporates. This process often leads to scale accumulation in water heaters, dishwashers, and faucets, which can affect efficiency and increase maintenance requirements. Identifying scale build-up is a practical way to assess water hardness, as it directly correlates with the mineral content in the water supply.

In contrast, discoloration of water could signify rust or sediment, low water pressure may result from various issues including clogs or pipe corrosion, and a cloudy water appearance often indicates the presence of air bubbles or sediment rather than mineral hardness. Each of these factors may affect water quality but does not specifically indicate the level of hardness like scale build-up does.