Water usage data, if measured with sufficient frequency, serves as a substantially transparent near-real-time indicator of human presence in a residential property.
Water usage data--recorded, transmitted and logged every hour--provides answers to these questions: Has anybody been home during the past hour? Has the home been empty during the past hour? What is the ongoing pattern of when people are at home and when they are away? Are more people than usual present in the home?
This is more true of water usage data than it is of electrical and gas usage data. Gas usage is largely automatic, as it is controlled by a thermostat. Electricity usage is also largely automatic, as it used by fridges, freezers, and other devices on timers. Water usage, on the other hand, occurs primarily when a person chooses to use water.
Every time you flush the toilet, within the hour, the city will be notified that you have used an appropriate amount of water for that task. How different is this from having mandatory motion sensors installed in every bathroom?
With water consumption measured monthly, the pattern of human presence is reported with very low resolution. When it is measured and transmitted hourly, the pattern of human presence is reported with very high resolution.