Water Sampling: Tools & Protocols

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

It is important to have good sampling methods when testing water so that we can determine the actual quality of the water. In this lesson, we will look at some of the tools and protocols for sampling water.

Clean and Representative Samples

Let's say you just made a big pot of soup, and you decide to taste it to make sure it is properly seasoned. You grab a spoon off the counter without paying attention and take a nice taste, only to spit it out saying it is way too salty! But then someone else comes along with a new spoon, takes a taste and says it isn't nearly salty enough. Is this just an extreme difference in taste preference? Or is something else going on? Perhaps, in your haste to grab a spoon, you grabbed a spoon which was covered in salt - thus contaminating your taste (or sample). Another possibility, is that the salt hadn't been stirred in properly, and you happened to take a sample of an area that was full of salt, while your friend sampled a spot that didn't have any salt.

Two big things that we need to take care of whenever we are sampling anything, is that the sample is clean (not contaminated by outside sources) and that the sample is a good representative of the entire population. In water sampling, these two issues are very important. Specific tools are used and protocols are in place to help ensure that clean and representative samples are taken.

Flowing and Still Water Sampling Location

In order to get a representative sample of flowing water, we need to take into account the fact that the flowing water will mix the water up as it goes along. If the water flows past certain contaminants (such as a road), the flowing water will pick up more contaminants at these points. So, the purpose of the sample needs to be taken into consideration. Are we simply trying to get a good picture of this particular river overall or are we trying to see how a specific factory is affecting the water?

Ideally the water will be sampled in areas with:

  • Uniform flow
  • Straight, stable bottom contours
  • Not directly around or beneath other structures such as bridges
  • Places with historical data

If the water is being tested for contamination, then it will, ideally, be sampled at a point far enough before the contamination (for a comparison) to ensure the flowing and mixing water hasn't mixed the contamination with the water already, and at a point far enough after the contamination enters the water to get a good mix of the contamination into the water as a whole.

In flowing water it is important to note discharge water in the proximity to our sample
Discharge pipe with water

Collecting from still water sources is much more straightforward than at flowing water sources. In these situations, you simply want to avoid boats, docks, and other contaminants (unless these are part of the purpose of the sample or part of the study). Locations with historical data are the best locations to sample.

Flowing and Still Water Sampling Methods

There are two methods used for sampling water: isokinetic and non-isokinetic. Isokinetic methods includes taking samples across a cross section of water to see what the water looks like at different depths. Non-isokinetic methods takes random points in the water and sample in those locations.

Still water typically requires several sampling sites and several depths, thus non-isokinetic methods are important. This is because the water is likely different from one point to the next because there is no flowing water to mix up the quality of the water into a homogeneous mixture.

Samples can be taken using churn and cone splitters, which are used to separate out suspended sediments in the water. Clean bags and samples must be used. For samples that will be tested for microbial loads, the equipment must be properly sterilized prior to use.

Well Water

There are typically two types of wells that water can be sampled from: monitor wells and water-supply wells. Monitor wells are wells that are made for the sole purpose of frequent testing. Water-supply wells are the wells that actually supply water for use and consumption. Frequent testing at the water-supply wells could contaminate those wells, thus the monitor wells are made in order to perform frequent testing, and only periodic testing is done on the water-supply wells unless something appears amiss in the monitor wells.

In water wells it is important to remember that the water is not exposed to the environment until we sample it
Water well

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