The department shall classify all potable water systems and facilities actually used or intended for use by the public, and all wastewater systems and facilities that discharge into publicly owned wastewater systems, or to receiving bodies of water, or on land used by others. The classification shall give due regard to

1. (1) the size and type of the systems and facilities;
2. (2) the character of water or wastewater to be treated;
3. (3) other physical conditions affecting the systems and facilities; and
4. (4) the skill, knowledge, and experience required of an operator.