Which items are essential to meet variable system demands in water supply?

To meet variable system demands in water supply, having adequate source capacity and treated water storage volume is crucial. This means that the water supply infrastructure must be able to provide enough water to meet varying consumer demands, which can change throughout the day or season.

Adequate source capacity ensures there is enough raw water available to be processed and treated. At the same time, sufficient treated water storage volume allows for the distribution of water even when demand spikes or during periods of high usage. This storage acts as a buffer, ensuring that supply can meet demand without interruption, especially during peak usage times or emergencies when the treatment plants might not be able to keep up with sudden increases in demand.

The other options, while they may play important roles in the overall management of a water system, do not directly address the fundamental need for a sufficient and reliable supply of water to meet changing demands.