How to take a Drinking Water Sample
A Total Coliform Present - E. coli Absent Sample by defined substrate method.
Total Coliform Present - E. coli Present Sample
Drinking Water Sampling Methods
How to Take a Drinking Water Sample for Laboratory Testing
Here's a bit of information that can be real helpful if you're in an apartment or if you're a homeowner and you want to take a water sample and have it analyzed. Sometimes folks don't read instructions that accompany the sample container or unknowingly "sabotage" their own results by not taking their sample properly.
There are certain protocols that should be adhered to when taking your drinking water sample, because the quality and reliability of results you get for drinking water analysis can be greatly affected by the manner in which the sample is taken.
There are many different types of contaminants and categories, but I'll just cover the main ones in this Hub. One of the most common and frequent tests performed is the Total Coliform test. This is the bacteriological analysis of your water, and the test is designed to determine if your source or well (drilled, dug, driven point, or municipal distribution), is, or recently has been compromised by surface water.
If you're source has been recently compromised directly by surface water (or surface water before it has had a chance to filter through enough earth to remove surface bacteria), then it may show positive for Total Coliform bacteria. Coliforms are part of the Enterobacteriacea Family, or Enterics for short. They are not typically pathogenic, or disease causing, but are kind of a "red flag" because if you find Coliforms in your drinking water then you don't know what other kinds of surface bacteria may have gotten in your well via the same route that the Coliform bacteria have gotten in there. Some types of surface bacteria you would be better off avoiding are, Klebsiella, Shigella, Giardia, Cryptosporidium, and Salmonella to name a fun few!
When taking the sample for Coliform analysis, run the cold water for about three to five minutes before sampling. Collect one hundred milliliters (about 4 ounces) in a bottle that is certified as sterile and comes from a laboratory that is certified for analyzing bacteria in drinking water. There may be a powder or pill in the sterile sample bottle - this is typically sodium thiosulfate and is there in case testing a municipal system that is chlorinated. It will reduce up to ten mg/L (parts per million) of chlorine so that if there are any bacteria in the sample, the residual chlorine won't kill them and then the laboratory can culture the bacteria. Sodium thiosulfate does not otherwise affect the sample results.
Do not set the cap down, or touch the rim of the sample bottle when filling. Don't let the dog lick it either, by the way! It's not a good idea to put a flame on the faucet end before sampling. Why? Glad you asked! Flames can leave carbon deposits on the in side of the faucet, which is a food source for certain heterotrophic bacteria. Now, these types of bacteria are not coliforms, but they can interfere with a coliform test if the lab was analyzing the sample via membrane filtration. Heterotropic bacteria are normally occurring flora, and if they get hold of a food source like carbon, they may grow enough to interfere with the test readings.
Once you've taken the sample and replaced the cover securely, deliver the sample to the lab
Most Coliform tests today are done by Presence or Absence methods, or MMO-MUG (Standard Methods for the Examination of Water and Wastewater, 19th Ed. 9223B). Once your sample has been taken, it must be analyzed within thirty hours to be considered a valid sample. Keep the sample cool (2-6 C.) if possible during hold time and in transit to the lab. Sample results usually take about twenty four hours, and both Total Coliform and E. coli results are simultaneously determined in this test. I'll give some more info in another Hub on coliform testing and what to do if you have Coliform and/or E. coli in your drinking water. So, see my video in this hub to get a demonstration of how to take a Coliform sample. It is the first one in the video. See an example below of the difference between a Total Coliform Present - E. coli Absent sample and a Total Coliform Present - E. coli Present sample. Notice that both samples are subjected to the UV light, but only the sample with the E. coli Present displays as bluish - green fluorescence. This is because the E. coli metabolize the MUG (4-methylumbelliferal-b-d-glucuronide) in the culture media and the hydrolysis, or cleaving of the MUG molecule creates a flurogenic product, as seen in the picture with the glowing vessel. This is indicitive of a water sample with E. coli.
The first step to taking samples for Lead to determine if there is lead in the home is done by not running the water in a tap like the kitchen or bathroom for at least six hours. Place the container directly under the tap and take the very first drops of cold water that come out. Typically, one liter is taken, but sixteen ounces is OK for homes. Then, let the water run for about three or four minutes, or until the temperature has stabilized, and then take another sample of the same size as the first one. The initial sample you drew was called a "first draw" sample, and if any lead is found in this sample, it is representative of the amount of lead you have in your home supply line. We then check the flush sample to see how much lead is coming from the source as opposed to the home. Typically, lead is introduced in the home water supply through lead solder in the distribution pipes, although certain brass alloy fixtures and fittings can be problematic as well. I see more lead in the home than lead in the source, usually. See the First Draw Lead Video.
Inorganics sampling is generally for contaminants like metals, nitrates, nitrites, and physical characteristics like hardness, alkalinity, conductivity, pH, and turbidity. Simply let the cold water run for 3-5 minutes and then fill the container. It is a good practice to rinse out the container once with the water you are testing as illustrated in the video for sampling inorganics. This is to re-assure you have rinsed anything out of the bottle that might cause cross-contamination. When receiving samples for metals, the lab will preserve the sample matrix with nitric acid, (HNO3) to a pH of less than 2.0 for at least 16 hours prior to analysis. Acidified samples may be held for up to six months without significant loss of sample components. Nitrate and nitrite samples should be kept cool until analysis as well, and must be analyzed within 48 hours from sample time to be considered valid. Nitrite (NO2) breaks down quickly via bacteriological action to nitrate (NO3), so it has to be run quickly. If you preserve the sample with sulfuric acid, you can get total nitrate and nitrite, but not individual species.
VOC's, or Volatile Organic Compounds can be found from underground storage tanks (UST's), or from petrol storage tanks located nearby that have leaked long enough to contaminate the aquifer. Examples of such contaminants would be Toluene, Benzene, Xylene, MTBE, and other petrochemicals and their additives. To properly sample for VOC's, you need some special sampling vials. The lab you use will give you two - 40 milliliter glass vials with rubber septa in the lid. Probably not something you have lying around the house! The vials may have such preservatives in them as sodium thiosulfate if testing a chlorinated system, and / or hydrochloric acid. You may also get a third vial that is pre-filled at the lab. It is called a trip blank and is used to detect any cross contamination from atmospheric exposure during the duration of the vials "lifetime" until they get to the lab. For example it would be a bad idea to fill you car with gasoline just before you go to take a VOC sample! Remember, these are Volatile chemical compounds (I love the smell of gasoline - I can't help it!), and that's why you need special vials to capture them -if they're there. So -when you fill the two - 40 mL. vials, fill them to the top so that there is no air bubble. To check, flip the vial over and look for a bubble -if you see one, just flip the vial back upright and add a few drops of water to just overfill, then carefully close the cover. Refer to the video to see an example of this procedure.
SOC's or Synthetic Organic Compounds are typically pesticides and herbicides and similar compounds. They have names like, Sylvex, Atrazine, and Glyphosate among others (about two pages worth of others). To take an SOC sample, you need two one-liter amber glass jars with teflon lined caps as well as six 40 mL. glass vials. The 40 mL. vials are similar to the VOC vials, except they will have different preservatives like MCAA (monochloroacetic acid) and some may be amber glass instead of clear glass. Fill without air bubbles as the VOC vials, and just fill the two amber glass one liter jars with cold water after letting the cold water run for about three to five minutes as above. Check out the video to see this sample taken as well.
I hope you enjoyed this Hub about drinking water sampling and found it useful!
After this typing, I'm thirsty - time for a cold glass of water! I like my water as fresh squeezed lemonade (extra sugar, please!)