At first glance, collecting a water sample seems to be as simple as following directions and selecting the right test. But what happens when a result comes back as an exceedance of a drinking water standard? Often, this leads to panic and the question of “what do I do now?”. Whether you are a private or public drinking water system, or on a private well, the next step should be a Source-to-Tap Investigation. WQI uses this approach to understand why and where problems originate, ultimately forming our recommendations on how to respond to the cause(s) of an issue rather than chasing the symptom(s).
The source of water varies depending on the water system. For buildings and homes attached to a private well, the source is the well, and more precisely the aquifer that supplies that well. For buildings and homes attached to a municipal water system, the source is water supplied by the water utility. Depending on conditions within the aquifer (or surface water, for some municipalities), source water quality can be vastly different between water systems and even between wells in a water system. The source water quality is the starting condition of water in a system or in part of a larger system. We anticipate water quality would not change throughout a well, a water distribution system, or within a plumbing system unless it Is acted upon by external factors. These external factors include, but are not limited to, disinfectant (type and concentration), corrosion, microbial or biofilm presence, pipe (materials, diameters, connections), water system configuration and plumbing system design (loops vs. branches, flow velocities). No two water systems are the same, and neither are the combination of factors in a system that can influence water quality.
Regardless of a water system’s characteristics, the Source-to-Tap approach is applicable and helpful in many of our project scenarios. This is why a sample that is collected following typical compliance instructions doesn’t always indicate what the water represents. By assessing how water changes from the source to the point-of-use (i.e. tap), WQI can determine where potential water quality issues arise and why they are an issue. To better illustrate these concepts, examples of investigation approaches are discussed below.
Coliform Issues in a Residential Plumbing System
Our first scenario consists of a residential client who has their water tested as part of a well pump replacement. Their sample came back positive for Coliforms and negative for E. coli. The pump installer collected the sample from a kitchen faucet after sterilizing the tap and flowing it for five minutes. This is a proper technique for collecting the sample, but we don’t know if the well pump was running at the time of collection (if it was, we don’t know how long it was pumping for) and if the sample represents a portion of the well (or which portion, for that matter), the line connecting the well to the home, the pressure tank, or the house plumbing system. While some homeowners may have historical testing records for us to compare to and determine whether this result is consistent with prior testing, in most cases we don’t have this information.
Our approach to this type of investigation would include collecting additional samples to determine if the aquifer (source of water) or an issue in the well (biofilm or defect) is the cause of the Coliform positive result. Budget is critical to our investigations, and we prefer to see two well samples at a minimum for analysis. However, if the client’s budget allows, we would also like to see samples after any in–home treatment (if present) as well as at the tap originally sampled. This allows us to see where the Coliforms are coming from and to track how counts of bacteria change (or don’t change) across samples. By comparing results across specific samples, we can provide recommendations with more confidence. The results will indicate if we should recommend a well cleaning, installation of in-home treatment, or look further into plumbing equipment, such as the pressure tank, to determine if it is working correctly or the cause.
Blue-Green Staining at Residential Taps
The second scenario is a homeowner supplied by a municipal system experiencing blue-green water and staining in their sinks and shower, which suggests copper plumbing corrosion. A simplified strategy could include a sample taken at the homeowner’s entry point (tap closest to entry of water to the home from the distribution system), a sample representing softened or treated water from the home (if applicable), a sample representing the client’s water heater, and a sample from a distant tap experiencing blue-green water and staining (hot and cold). This approach determines where in the water system the issue starts and if the issue is in the hot water, cold water or both.
This strategy allows us to track how the water quality and corrosivity changes from the utility to the point of use and determine if recommendations should address the municipality’s infrastructure or the private client’s property. Municipal water systems may produce water which meets all regulations but still leads to water quality or corrosion issues within a client’s property. Conversely, if the municipal system’s water meets regulations, it can still be under the influence of biofilm in the distribution system to influence water quality in the plumbing. If samples were not collected in the source-to-tap approach, it would be difficult to clearly distinguish which aspect(s) of the system needs to be addressed.
Additional Benefits of Source-To-Tap Approach
WQI’s Source-to-Tap investigative approach is a concept that uses custom strategies due to the unique nature of every water system. The custom sampling, which is based on the perceived problem(s) and on system design and operation, helps target the true source of an issue. While more samples add cost compared to a “one sample approach,” they lead to a thorough analysis which can ultimately save the client money. Investigations that save long-term client expenses generally include the following:
- Performing periodic well rehabilitation to reduce iron, arsenic, nitrate or radium, or to solve a coliform issue, instead of drilling a new well (residential and municipal)
- Using alternate materials and installation approaches to solve corrosion in wells
- Modifying or adding water treatment instead of installing a new water source (well or connecting to city distribution system)
- Cleaning plumbing systems and performing routine maintenance instead of full replacement of plumbing or equipment
In both of the scenarios described in this article, it would be extremely difficult to reach a conclusion and give our clients recommendations without the Source-to-Tap strategy. Not only is it important to know what each sample specifically represents, we also need the ability to compare samples within a project to determine what is causing water to change to cause observed issues. At WQI, we find that many changes in water quality are attributed to naturally forming biofilm, the presence of nutrients and stagnant or low use conditions, which are not regulated by current Standards. Many water issues we investigate cannot be solved by simply looking at results from a regulatory standpoint. Investigating the role of biofilm and tracing water from its source to point-of-use helps reveal underlying issues that would otherwise go unnoticed with regulatory testing. Water quality issues are not isolated incidents in systems, which is why examining how water changes from the source to the tap has allowed WQI to help clients solve issues left unsolved by the current industry’s approach to water testing. Contact us today to discover how our tailor-made investigations can help solve your water quality issues.
Authored by: Emily Hefty-Dieckhoff