Which plumbing fixture has the lowest typical water demand?

The drinking fountain typically has the lowest water demand among the listed plumbing fixtures. This is primarily because drinking fountains are designed to provide a limited amount of water for consumption and are not used for filling large containers or for extended periods. Users typically take quick sips, which results in low overall water usage.

In comparison, bathtubs and shower heads are designed for bathing and usually deliver larger volumes of water—baths often require a significant amount of water to fill the tub, while showers can consume considerable water, especially if they are longer in duration. Sink faucets can also be used for various tasks such as washing hands, dishes, or food, leading to higher water usage depending on how long they are left running. Thus, in terms of water demand for regular usage, drinking fountains stand out as the fixture with the least requirement.