What will cause head loss across a filter to increase?

The increase in head loss across a filter is primarily associated with the build-up of solids. As water passes through a filter, suspended particles and impurities start to collect on the filter medium. This accumulation of solids creates additional resistance to the flow of water, which translates into increased head loss. Essentially, the more particles that are trapped within the filter, the more energy is required to push the water through, thereby leading to a higher head loss.

In contrast, a decrease in water temperature may lead to a slight reduction in viscosity but doesn't have a direct correlation with head loss due to solids accumulation. Higher water clarity generally indicates fewer suspended particles in the water, which would lead to lower head loss. Lastly, a reduction in water flow typically results in less turbulence and can actually decrease head loss, as the pressure drop across the filter is more significant at higher flow rates. Thus, the accumulation of solids is the key factor causing an increase in head loss across a filter.