By Chang R. Lee, Ph.D., Phillip Terrazas and Prosy Abarquez-Delacruz
Summary: This two-part series expands on an article written by Larry Eils, director of the National Automatic Merchandising Association (NAMA), on surveys in California in 1998 and 1999 on water quality from vending machines (“Good News is No News,” WC&P, October 1999). In Part 1, heterotrophic bacteria results from the two studies were compared. Here, a discussion of coliforms and total dissolved solids (TDS) levels measured in the studies and suggestions to improve the quality of vended water are offered.
Coliform bacteria are much less common in the environment than heterotrophic bacteria, measured via heterotrophic plate counts (HPC). Coliform reporting depends on laboratory growth media and procedures used for testing. Total coliform determinations are one of the oldest and most commonly used measurements of the sanitary quality of water.
Coliform, E. coli testing
A presence/absence (P/A) test—usually used for screening—is reported as total coliform positive if any coliforms are detected and an enumeration test reports the most probable number (MPN) of coliforms that are statistically most likely to be present in 100-milliliter (ml) sample. Fecal coliforms and E. coli can also be detected by some P/A tests and enumerated by the MPN test procedure. Procedures using several Colilert growth media (i.e., chromogenic, defined substrate test systems) are increasingly being used with water to perform P/A tests and for enumeration. The Colilert multiple tube procedure is used with water to perform enumeration tests. Multiple tube fermentation methods use much older technology and are slower, more expensive and less sensitive than Colilert procedures. Although inaccurate, some testing laboratories consider fecal coliforms and E. coli as interchangeable when reporting P/A and enumeration test results.
Water vending machines (WVMs) are subject to state and federal bottled water laws which provide limits on total number of coliforms that may be present. The most common limit used is “not greater than 2.2 MPN total coliforms/100 ml.” There’s no separate standard for fecal coliform or E. coli. On the contrary, large public drinking water systems are subject to state primary drinking water standards which require the suppliers to test a specified number of water samples monthly for total coliforms; small systems test a lesser number of samples. The standards for large public drinking water systems are as follows: If more than five percent of the monthly tests are total coliform positive, the water supplier—1) exceeds the standard; 2) must notify water users about the problem; and 3) must retest with additional repeat samples. If any of the repeat samples are fecal coliform positive or E. coli positive notice must be made more quickly and with more urgent wording.1 Small systems are subject to slightly different standards.
Each first draw sample and source water sample was initially screened for total coliforms using a Colilert P/A test. If a first draw sample was positive for total coliforms on the P/A test, a repeat first draw sample and a second draw sample were obtained from the WVM in most cases within 24 hours and tested both for total coliforms using a Colilert enumeration test. The unit exceeded the total coliform limit if enumeration testing showed greater than 2.2 MPN total coliforms/100 ml in either sample. If a source water sample was total coliform positive on the P/A test, testing results were forwarded for follow-up to the appropriate public drinking water districts. As shown in Table 1, 10 source water (public drinking water) samples were total coliform positive on the P/A test, while first draw samples from 11 were total coliform positive on the P/A test (none greater than 10,000 colony forming units per milliliter, or CFU/ml). Enumeration testing of the 11 repeat first draw and 11 second draw samples from the total coliform positive WVMs showed one of the units exceeded the total coliform limit on the repeat first draw and on the second draw. Both samples were negative for fecal coliforms. FDB sent a regulatory letter to the responsible operator requesting corrective action be taken. The operator sanitized the unit and provided FDB with testing results that showed samples from it to be negative for total coliforms. FDB follow-up testing of the units confirmed they were negative for total coliforms.
TDS consist mostly of magnesium, sodium, calcium and other minerals. Higher levels of certain minerals in water are desirable, up to a certain amount, for taste (water without minerals tastes “flat” while water with excessive minerals, has unpleasant taste). “Purified water” contains especially low levels of minerals and is preferred by some consumers for use in ironing, battery water replenishment and plant watering. State law requires vended water to contain less than 10 milligrams per liter (mg/L) of TDS if the water is claimed to be “purified water.” WVMs that make “purified water” claims have a treatment step (mostly reverse osmosis) designed to remove minerals present in the source water.
Each WVM was inspected to determine if it made “purified water” claims. Twenty-eight, or 3.5 percent of those sampled, made such claims. The additional second draw samples taken from these were tested to see if they met the 10 mg/L limit for TDS. Table 2 shows that 25 percent exceeded the limit.
The inspection also showed that: 1) required self-closing doors were missing from 247 machines, or 31 percent; 2) required doors were inoperative on 155, or 20 percent; and 3) some required labeling was missing from 146, or 18 percent. Theft and vandalism appear to be the major cause of the missing or inoperative doors.
The average HPC statewide testing result for first draw vended water samples was in close agreement with that of the local agency when the agency’s raw data were re-computed for a fairer evaluation (see Part 1, WC&P, February 2000). The HPCs for second draw samples approached the HPCs of the source water, indicating that the relatively high HPCs in some first draw samples was due more to re-growth of bacteria that survived disinfection than to failure of the disinfection method. The built-in ultraviolet (UV) light reduces the number of bacteria substantially but does not destroy all.
From these data, it’s concluded that vended water is safe and of good quality; and additional regulatory requirements for WVMs are unnecessary. However, three quality areas deserve more attention by operators: 1) HPC re-growth sometimes occurred in the tubing between the UV light and the dispensing spout of WVMs, and re-growth can be reduced by changes in WVM design or maintenance procedure; 2) operators of WVMs dispensing “purified water” need to assure that sufficient minerals are removed from the source water; and 3) operators need to better protect machines from theft and vandalism of the self-closing doors and provide all required informative labeling on WVMs.
- Title 22, California Code of Regulations, Section 64426.1
About the authors
Dr. Chang R. Lee is a scientist for the California Department of Health Services’ Food and Drug Branch (FDB), coordinating the state’s bottled and vended water programs. His doctorate in food science is from Ohio State University and he holds five U.S. Patents and five foreign patents. He coordinated this statewide vended water survey and was responsible for results interpretation and final report preparation. Lee can be reached at (916) 327-8041 or email: [email protected]
Phillip Terrazas is a senior investigator for the FDB and has worked for the agency for four years. He conducts investigations at wholesale food manufacturers, water bottling operations and other related facilities. He played a major role in the development, planning, implementation and oversight of this survey. His bachelor’s degree in biology is from California State Polytechnic University, Pomona, and his master’s in public health degree in environmental health from the University of California-Los Angeles School of Public Health. Terrazas can be reached at (213) 580-5745 or email: [email protected]
Prosy Abarquez-Delacruz is a regional administrator for the FDB, providing regulatory oversight to processed foods manufacturers and distributors through a public health-law enforcement team of supervisors and investigators in Southern California. She holds both a bachelor’s degree in food technology from the University of the Philippines and a juris-doctorate degree from Whittier College School of Law in Los Angeles. She has over 20 years of experience in regulatory affairs and played a critical role in the above statewide vended water survey. Abarquez-Delacruz can be reached at (213) 580-5720 or email: [email protected]