Which factor can contribute significantly to a decrease in water flow?

Clogged pipes or fittings can significantly decrease water flow because they impede the smooth passage of water through the plumbing system. When debris, mineral deposits, or other blockages accumulate in pipes, they create resistance that reduces the overall flow rate. This can lead to decreased water pressure and can affect the efficiency of the system, making it challenging for the water to reach fixtures or appliances that require it.

Regular maintenance of the system is essential to prevent such clogs but does not itself contribute to a decrease in flow when performed correctly. Excessive water usage during peak hours might create temporary shortages or pressures but is not a direct cause of a decrease in water flow itself; it more often relates to demand on the system rather than the physical flow capacity. High water tank levels typically indicate sufficient supply and would not inherently decrease flow. Thus, the most direct contributor to decreased water flow in this context is indeed clogged pipes or fittings.