Which type of water doesn't have to be sampled?

The correct answer is focused on the regulation and safety standards concerning drinking water. Drinking water is subject to stringent sampling and testing requirements to ensure it meets health and safety standards. Agencies have specific protocols in place aimed at preventing contamination and ensuring the water's integrity before it is supplied for consumption.

In contrast, while swimming water, industrial process water, and rainwater may still have quality considerations, they generally are governed by different sets of regulations that may not require the same level of routine sampling as drinking water. For example, water for swimming may require sampling to ensure safety for recreational use, and industrial water may be tested based on operational requirements. Rainwater collection and use typically do not fall under mandatory sampling requirements for public health but may have guidelines that can vary significantly based on local regulations.

Thus, drinkable water's comprehensive oversight and necessity for regular monitoring underline why this option stands out as requiring specific sampling protocols.