Public Water System Classifications
The Idaho Rules for Public Drinking Water Systems require that DEQ classify all community, nontransient noncommunity, and surface water public drinking water systems with a treatment and/or distribution classification based on indicators of potential health risk. Criteria used to determine the potential health risks include the system's complexity, size, and source water for treatment facilities; complexity and size of distribution systems; and other criteria deemed appropriate. Systems are classified by type (treatment or distribution) and class. Classifications range from Very Small to Class I, II, III, or IV. The rules also require that public drinking water systems be staffed by licensed operators based on the system classification.
Determining a System's Classification
Each public water system’s owner must calculate the system's treatment and/or distribution classification to ensure its operators, and in particular, the responsible and substitute responsible charge operators, are properly licensed.
Distribution System Classification
Based on complexity and population served as follows:
- Very Small Water System (VSWS) * see definition below
- Distribution Class I - 501 to 1,500 (DWD1)
- Distribution Class II - 1,501 to 15,000 (DWD2)
- Distribution Class III - 15,001 to 50,000 (DWD3)
- Distribution Class IV - 50,001 and greater (DWD4)
* Very Small Public Drinking Water System – A community or nontransient non-community public water system that serves 500 persons or less and has no treatment other than disinfection ** or has only treatment, which does not require any chemical treatment, process adjustment, backwashing or media regeneration by an operator. (e.g. calcium carbonate filters, granular activated carbon filters, cartridge filters, ion exchangers.)
** Disinfection – Introduction of chlorine or other agent or process approved by DEQ, in sufficient concentration and for the time required to kill or inactivate pathogenic and indicator organisms.
Treatment System Classification
Based on a point matrix associated to population, primary source type, and treatment processes associated to public water system treatment plants that are tracked in DEQ’s Safe Drinking Water Information System (SDWIS):
- Treatment Class I – 0 to 30 points (DWT1)
- Treatment Class II – 31 to 55 points (DWT2)
- Treatment Class III – 56 to 75 points (DWT3)
- Treatment Class IV - 76 points and greater (DWT4)
A worksheet has been developed to assist the owner of a public water system in determining system classification. The worksheet must be filled out and submitted to DEQ every five years or any time a substantive change or upgrade is made to the treatment or distribution system. Based on the information provided in the worksheet, DEQ determines the system's classification.
- Drinking Water Distribution and Treatment System Classification Worksheet - (This electronic form opens best in Internet Explorer)
Current Public Drinking Water System Classifications
DEQ updates a list of drinking water treatment and distribution system classifications daily.
Note: This list is a snapshot in time according to the date shown on the list.
Drinking Water System Name/Address Changes
The drinking water system owner or the owner's designee can add a contact or update address, telephone number, or e-mail information by using the "Change Water System Information" button on the PWS Switchboard.