Sample Collection Techniques For Coliform Analysis
Sample bottles from Public Health Laboratories contain a chlorine neutralizer in liquid or crystalline form. They are sterile and ready for used when shipped. Do not rinse contents from the container and keep bottle closed until it is to be filled.
Sample Collection Procedures
- Assemble all of the sampling supplies before you begin and wash your hands thoroughly before handling supplies.
- Go to the sampling location(s) specified in the sampling plan. The sample should be taken from a clean smooth-nosed cold water tap if possible. Avoid drinking fountains, leaky faucets and frost-proof yard hydrants, since it is not practical to sterilize these fixtures.
- If possible, remove any aerators, strainers, or hoses, because they may harbor bacteria.
- Open the cold water tap (or hot water if a mixing faucet is used) for about three minutes before collecting the sample. This should adequately clear the water line.
- Flame-sterilize the tap or chemically disinfect the tap. Do not flame-sterilize if the tap is plastic or if aerators are attached. Disinfect the tap by thoroughly rinsing both the inside and outside of the tap with a mixture of 50 percent bleach and 50 percent tap water. Take extreme care with strong bleach (oxidizing) solutions.
- Flush the tap for an additional three minutes with cold water and reduce to a gentle flow to about the width of a pencil. Do not change the water flow once you have started sampling. It could dislodge microbial growth.
- Grasp the cap along top edge and remove carefully. Do not touch the inside with your fingers. Hold the bottle in one hand and the cap in the other. Do not lay the cap down or put it in a pocket! Also, take care not to contaminate the sterile bottle or cap with your fingers or permit the faucet to touch the inside of the bottle.
- Fill bottle to the 100 ml line or to a little above the black line. Hold the bottle so water entering the bottle will not come in contact with your hands. Samples will not be tested if there is less than one-half inch air space in the bottle. Then place the cap on the bottle and screw it down tightly.
- Fill out the water analyses card in waterproof ink.
If you use the Missouri Department of Health and Senior Services - Contract Courier to deliver your samples, the following tip may help. The contract courier cannot pick samples up before 10:30 a.m. Therefore, to be certain of meeting the holding times of 30 hours, it is important to collect your samples that morning and have them dropped off at the contract courier pickup point by 10:30 a.m. Contact the Department of Natural Resources’ Public Drinking Water Branch for more information at 573-751-5331. If you use the U.S. Postal Service, remember the 30-hour time limit starts when the sample was collected. The department recommends you use Priority Mail or faster to mail water samples.
- Sometimes, in spite of taking all precautions, you may get a call from us or results by mail telling you that you have Total Coliform or E.coli bacteria in your water. You will then be given specific instructions that may include collecting repeat samples to confirm that the first routine sample was not a sampling error.
- Whenever you have a sample test positive for coliform bacteria, you are required to collect five routine samples the following month. A maximum contaminant level, or MCL, violation is issued to a facility when two or more monthly bacteriological samples have coliform or E.coli bacteria present. Please call your local Department of Natural Resources Regional Office to discuss the procedure.
- Sample results are available within four or five days on Drinking Water Watch