(1) Swimming pool and spa waters must be maintained with a chemical quality sufficient to prevent levels of bacteria from exceeding 200 bacteria per milliliter as determined by the total standard (35 E C) agar plate count, or the presence of more than four coliform bacteria per 100 milliliters by the membrane filter technique, or show a positive test (confirmed test) for coliform organisms in any of five 10-milliliter portions of a sample when the pool is in use. All samples must be collected, dechlorinated, and examined in accordance with the procedures outlined in 9213 of the Standard Methods for the Examination of Water and Wastewater (APHA, AWA, WEF) . Not more than two consecutive samples in a 1-month period may exceed the levels specified.

(2) Chemicals added to the swimming pool or spa water shall not cause irritation of the eyes, skin or mucous membranes of the bathers.

(3) All swimming pools and spas, when open or in use, must be continuously disinfected by a chemical which imparts a residual effect and must be maintained in an alkaline condition. Disinfection must be handled by mechanical means. A chlorine residual of 1.0-5.0 ( 3.0-5.0 ppm recommended) must be maintained in the pool at all times. A difference of .5 ppm between free and total chlorine readings in swimming pools requires super-chlorination. Spa pools must be superchlorinated as necessary which will be indicated by use of a DPD test kit. Spa pools which utilize a combination ozone and bromine disinfection method are not required to superchlorinate.

(4) If halogens other than chlorine are used, residuals of equivalent disinfectant strength shall be maintained.

(5) The regulatory authority may accept other disinfecting materials or methods when they are demonstrated to provide a readily measurable residual and to otherwise be equally effective to the chlorine concentration required herein, and not be dangerous to the public health. Regulatory authority approval must be given prior to utilizing other disinfecting materials.

(6) Chemicals used in controlling algae growth shall not pose a risk to public health or contribute toxic properties to the water.

(7) The water shall have sufficient clarity at all times so that a black disc, 6 inches in diameter, is clearly visible and sharply defined when placed on a white field at the deepest point of the swimming pool or spa.

(8) Swimming pool and spa waters shall be maintained at a pH of not less than 7.2 and not greater than 7.8.

(9) The total alkalinity (TA) of the water must be at least 80 ppm and no greater than 200 ppm. TA levels are 100-125 ppm for plaster pools, 80-150 ppm for spas and 125-150 ppm for painted and fiberglass pools. Pools must be in chemical balance, or water balance, as determined by the saturation index.

(a) Calcium hardness readings must be taken and recorded at least weekly to determine water chemical balance. Chemical balance, as determined by the saturation index, must be tested at a minimum of once per week on pools, or more frequently as necessitated by the conditions of the pool. If a spa does not meet the TA level requirements for saturation index and chemical balance and is not chemically corrected, the spa water must be completely exchanged with fresh make up water according to one of the frequency standards in ARM 37.111.1152(8) .

(b) The saturation index reading must be maintained between -.5 and +.5. Adjustments must be made to the pool water over the next 24 hours as determined by the saturation index.

(c) The following table must be used to determine the saturation index:

Saturation Index = pH + TF + CF + AF - 12.1

Numerical Values For Formula

TEMP ºF	TF	Calcium Hardness Expressed   AS PPM CaCO3	CF	Total Alkalinity Expressed   AS PPM CaCO3	AF
32	0.0	5	0.3	5	0.7
37	0.1	25	1.0	25	1.4
46	0.2	50	1.3	50	1.7
53	0.3	75	1.5	75	1.9
60	0.4	100	1.6	100	2.0
66	0.5	150	1.8	150	2.2
76	0.6	200	1.9	200	2.3
84	0.7	300	2.1	300	2.5
94	0.8	400	2.2	400	2.6
105	0.9	800	2.5	800	2.9
128	1.0	1,000	2.6	1,000	3.0

 

Index between -0.5 and +0.5 is balanced water.

Over +0.5 is scale forming.

Below -0.5 is corrosive.

 

Key: TF = temperature factor

         CF = calcium factor

         AF = alkalinity factor

(10) The department hereby adopts and incorporates by reference section 9213 of the Standard Methods for the Examination of Water and Wastewater by the American Public Health Association, the American Waterworks Association, and the Water Environmental Federation (APHA, AWA, WEF) , 19th Edition, 1995, which establishes test procedures and what to test for in recreational waters, including swimming pools and public bathing places that are not swimming pools. Copies of section 9213 of the Standard Methods for the Examination of Water and Wastewater (APHA, AWA, WEF) may be obtained from the Department of Public Health and Human Services, Health Policy and Services Division, Food and Consumer Safety Section, 1400 Broadway, P.O. Box 202951, Helena, Montana, 59620-2951.