Kirsten Scott, Aclarus Research & QA Lead

 

Water Sampling 101

A crucial first step in determining an ozone treatment solution is to provide an accurate water sample. Kirsten Scott, Aclarus Research and Quality Assurance Lead, explains the requirements necessary for providing water samples.

If you have never worked in a lab or a water treatment facility before, you are likely unaware of the complexities of water sample analysis and all of its requirements. There are many aspects that must be taken into account in order to ensure water analysis results are accurate. These aspects include sampling location and procedures, specific volumes, preservation requirements, container requirements, storage/shipping temperature requirements, and holding time requirements (the time between a sampling event and time of analysis).

The first step in any sampling event, it to assess the required outcome; are you interested in general water quality or are you required to meet and report to municipal by-laws? Naturally, that later is a much more complicated and involved task, therefore it is best to develop a sampling and analysis plan. The plan will help you define what analysis is required based on the by-law you are required to meet, once defined, the volumes, bottles and preservation requirements should be acquired from your accredited laboratory providing the analysis service. Your next steps will be to determine your sample locations, and sampling procedures as well as establish important factors such as whether or not the water source is chlorinated, is the sampling time indicative of your target, ie if you’re experiencing low water quality in the height of the summer, you wouldn’t want to take samples in November when you are not experiencing elevated levels. Your sample location is also important; ensure your sample location properly represents your intention, define whether you require raw water (before treatment) or treated water, or are you required to take multiple sample locations? A well-developed sampling plan will be a great resource to guide you through the tedious and detailed process.

 

Bottles

It is always important to pre-order bottles from the lab performing the analysis before taking on a sampling event. The lab will provide you with the required bottles that contains the required preservation, proper bottle material and volumes needed to ensure accurate analysis. Most samples can be placed in a plastic (PET) bottle; however, many require special materials because the sample may degrade when subjected to air or light, or certain materials may contaminate the sample or cause interference during analysis. Sample containers can be plastic, high density polyethylene, glass, amber glass, opaque plastic, or sterile plastic; furthermore, samples may require the caps to be plastic, teflon or phenolic-free. Each parameter has different requirements, your analyzing lab is the best source to ensure you have the correct sampling vessels.

 

Preservation, Volumes and Holding Times

Proper preservation practices are parameter and method specific and should be used as soon as possible after sample collection. A preservation technique often overlooked is the storage temperature of the sample; all samples should be stored and shipped at 4-6°C or kept on ice until delivery to the lab. Other preservation techniques include the use of filtration, acids, bases, or other chemicals at specific concentrations. The preservation not only maintains the current state of the sample but extends that state long enough to allow for analysis to take place. For example, a sample collected for Oil and Grease requires 1000mL of sample to be stored in an amber glass bottle with a teflon cap and adjusted to a pH of less than 2. Unpreserved, the sample should be analyzed within 7 days of collection, however when preserved appropriately, the lab can analyse the sample within 30 days of the sample collection.

Parameters that do not have specified preservation techniques or have very short holding times are the most problematic as they require preplanning to ensure timely delivery to the lab. Here is a list of some of parameters that are commonly sampled but require quick turn-around.

 

Each parameter has a different method for analysis and therefore the volume requirements vary greatly.  Consider analyzing for Total Suspended Solids (TSS), this analysis requires filtering the water sample to collect the particulate which is then dried and weighed.  The cleaner the water sample is, the less TSS is present in the water, therefore it must be ensured that enough volume is submitted for filtering for accurate results.  For this analysis, it is recommended to submit 1000mL of sample.  If the sample is particularly dirty or from surface water, you are likely to get away with only submitting 300mL of sample.  With proper storage, preservatives are not required for TSS, however the analysis should be performed within 7 days of the sampling event.

 

Sampling for Biological Contamination

E.coli, and total coliforms are used as indicators to measure the degree of pollution in your water, while coliforms are not likely to cause illness, their presence indicates contamination with more harmful microorganisms.  E.coli is the major species of fecal coliforms (coliforms present specifically in the gut and feces of warm-blooded animals).  Total coliforms and E.coli analysis is quantified with Colony Forming Units (CFU) in a 100mL of sample.  CFU’s is an estimation of cells that are viable enough to form colonies that are visible to the naked eye.  The regulatory limit for drinking water is <1 CFU/100mL of sample, meaning both E.coli and total coliforms should be non-detectable in order to be deemed safe to drink.

Biological analysis is sensitive, after all they are analyzing living organisms which we want to keep alive, but also want to prevent reproduction so that the analysis is accurate and represents the population at time of sampling.  The following are the requirements for sampling, preservation, storage and holding time:

  • Wear latex gloves to avoid contaminating your sample

  • Allow cold water to run for approximately 5 minutes before taking a sample

  • Sample bottle should be a sterile bottle provided by the lab performing analysis

  • Do not open the sample bottle until you’re ready to take sample

  • Do not touch the inside of the collection bottle, or set down the lid

  • Ensure the sample bottle contains Sodium Thiosulfate (preservative)

  • Do not overflow the bottle as this will lead to loss of the preservative

  • Fill the bottle to the 100mL sample line, tighten lid until leak tight immediately

  • Do not aggressively shake the sample bottle

  • Immediately transfer sample to a fridge or cooler and keep the sample at approximately 4-6°C

  • The sample should be delivered to the lab within 24 hours as the sample needs to be analyzed within 24 to 48 hours (some labs may differ in holding time, be sure to verify with the lab)

 

For more detailed information on water sampling please contact Kirsten Scott kscott@aclarusozone.com.