How to Analyze Your Water Testing Results

Routine water testing is a necessity for industrial water systems.  These include cooling towers, steam boilers, hot water boilers, drinking water, wastewater, ultra-pure water, and others.  Analyzing water samples is key to understanding the general conditions of the treated system.  The samples are not only indicative of the treatment levels, but also the levels of other constituents that are indicators of the general condition of the treated system and program performance.  The water testing will also ensure that the system is being operated within the prescribed parameters.

To ensure that decisions made around the results of the water testing are based on accurate information, it is important to consider the impact of interferences and other factors that could affect the accuracy of the test results.

What Should Water Be Tested For?

While the specific testing parameters and ranges can vary by the type of system being sampled, the majority are common between systems.  Along with the common testing parameters, there are also testing parameters that are specific to the type of treated system and the treatment program associated with the system.

Common, non-system-specific testing parameters may include:

  • Conductivity
  • Hardness (Calcium, Total, and Magnesium)
  • Alkalinity (Total)
  • pH

In addition to the parameters listed above, the following system-specific parameters are common to the system type.

Cooling Towers

  • Phosphonates
  • Polyphosphate
  • Chlorides
  • Orthophosphate
  • Molybdate
  • PTSA
  • Oxidizing biocide level (total chlorine, bromine, free chlorine, chlorine dioxide, etc.)
  • Non-oxidizing biocide level
  • Copper
  • Silica
  • Azole Level (TTA, BZT, HSA etc.)
  • Biological testing (dip-slides, ATP, etc.)

Steam Boilers

  • Fluorescing tracers
  • Polymers
  • Phosphate
  • Sulfite
  • Amines
  • Dissolved oxygen
  • Alkalinity (P and OH)
  • Iron
  • Low Level Hardness

Heating Boilers (Hot Water Boilers)

  • Nitrite
  • Molybdate
  • Silica
  • Copper
  • Iron
  • Filming Amines
  • Tannins


  • Polymer
  • Various metals
  • Turbidity
  • Jar Testing (product performance)
  • Treatment specific testing
  • Biological testing (dip-slides, ATP, etc.)
  • Chlorine (discharge water)

Drinking Water

  • Oxidizing biocide level (total chlorine, bromine, free chlorine, chlorine dioxide, chloramines, etc.)
  • Biological testing (dip-slides, ATP, etc.)
  • Copper
  • Iron

The examples above are a few examples of industrial water systems.  These systems are found across many industries related to comfort heating or cooling, energy, food sanitation, clean in place, food preparation, manufacturing, laundry, agriculture and many others.

How to Interpret Your Water Test Results 

The water analysis gives the water treatment professionals and system operators a snapshot of

the system conditions.  Interpreting the testing results is key to understanding the overall product and system performance.  Each tested parameter will have a control range or recommended range based on:

  • The water treatment professional’s knowledge of the system
  • Quality of the make-up water
  • Water limitations
  • Discharge limitations
  • Overall performance expectations.

Interpreting the test results should be done using all the testing results.  Many parameters are directly linked to each other and will move up and/or down with another parameter.

An example of this is PTSA and phosphonate in a cooling tower system.  Since PTSA is present in the system as a tracer or indicator of the amount of corrosion/scale inhibitor in the system, the phosphonate level should correlate directly to the amount of PTSA in the system.  For example, if the PTSA level is within the recommended control limits and the phosphonate is over or under the limits, the calibration of the PTSA sensor should be examined.  If the PTSA sensor is properly calibrated, the phosphonate level should be evaluated further as this could be indicative of other system and or product concerns.

Since parameters such as pH, hardness, conductivity, and alkalinity are commonly used to determine important system conditions such as cycles of concentration, close attention should be paid to these and the relationship between them.  Any variation of these parameters from the prescribed control limits should be compared with the overall water analysis.

An example of this is the relationship between conductivity and alkalinity when they are used as indicators for cycles of concentration.  In a water system with a make-up conductivity value of 300 mmhos and 100 ppm of total alkalinity, at four cycles of concentration the system conductivity should be approximately 1200 mmhos and 400 ppm of total alkalinity.  At these levels, the numbers balance with the cycles of concentration.  However, if the pH of the system is being adjusted by the addition of acid or caustic, the alkalinity of the system will not correlate to the conductivity cycles and cannot be used to estimate the cycles of concentration.

Another example is the relationship between hardness and conductivity when used in the same way as our previous example.  If a system has a make-up conductivity of 300 mmhos and a total hardness of 100 ppm, at four cycles of concentration, the conductivity should be approximately 1200 mmhos and the total hardness should be approximately 400 ppm.  If the hardness level is noticeably less, the testing should be evaluated further.  Examples of the conditions that could impact this balance would be a variation in the make-up water chemistry over time or the loss of hardness due to scale formation.

If the testing results do not make sense or do not fit a known scenario, a close examination of the testing procedures may be warranted to ensure that the information is accurate and can be acted upon appropriately.

Interferences That Can Impact Water Testing Results

It is important to understand that there are a variety of conditions and factors that can impact the accuracy of the water sample testing results.  These are generally referred to as interferences and can be related to chemical, mechanical or human issues. The number of interferences is too numerous to list, but there are several examples of these that apply to routine testing.  These may include interferences by products being added to the treated system or even the tested parameter itself. With 80-85% of errors related to water quality results being impacted by user error, it’s important to follow best practices to minimize and eliminate errors

Here are some essential steps to follow:

  • Use clean equipment – properly rinsing and cleaning equipment before and after testing helps to eliminate contamination from previous tests.
  • Collect accurate samples – there are a variety of factors around sample collection. For starters, it’s important to make sure you collect a sample that is representative of the entire system. When performing your test, pouring an accurate sample size is also important. Small errors in sample collection can have a big impact on your results.
  • Use proper testing technique – Holding bottles vertically for consistent drop size, proper lighting and simply following written procedures are very important. While they may seem minor, they can add up in a big way.
  • Interpreting your results – making sure you are using the proper factors and expressing your results properly during your test is also important. Is your test expressing results as sulfite or sodium sulfite or nitrite vs sodium nitrite? When calculating and interpreting your water testing results, these matter.

A common chemical interference is seen in the testing of chlorine using the DPD method.  While DPD is commonly used to determine the amount of chlorine in a sample, higher levels of chlorine can cause bleaching of the reagent and mask the test results.  The phenomenon can occur with as little as 5 ppm of chlorine in the sample.  To mitigate this problem, the sample can be diluted, and a multiplier can be applied to the results to compensate for the dilution.

An example of physical interference is seen when a sulfite test is run on a boiler water sample when waiting for an extended period between sampling and testing.  Exposure to air for an extended period can result in a lower-than-expected result.  To avoid this, the sample container should be capped and the sample tested as soon as possible. It’s also critical that sulfite samples be cooled before testing. Not following these important steps will lead to inaccurate results.

Though the list of possible interferences can be overwhelming, many common interferences are listed within the test kit documentation and can be easily avoided by following the basic procedures outlined in the testing instruction.

Analyze Your Water Supply With Customizable AquaPhoenix Test Kits

AquaPhoenix Scientific offers standard and custom test kit solutions for every water treatment need.  We can formulate custom testing procedures designed around your specific products and application needs. Our EndPoint ID testing procedures are easy to follow with photographic step-by-step instructions to make testing simple and effective for users of all experience levels.  By including testing tips, safety reminders and interferences directly in our test procedures, you can have confidence knowing you are setting your team and customers up for success from the start.

Contact AquaPhoenix Scientific for a quote or reach out to your water treatment professional for questions or concerns about specific testing parameters.