Testing Choices For Watershapers
Watershapers pour engineering skill, architectural know-how, building expertise, and artistic vision into projects clients expect to enjoy for years to come. Many factors impact the longevity and successful operation of a watershape, but one element tops all others: water quality. Water must be balanced to prevent damage to surfaces and equipment as well as sanitized to protect the health of people who come in contact with it. In living systems, such as ponds and streams, the water's characteristics also must be managed to prevent harm to aquatic plants and animals. So, how can you ensure quality water? Simply stated, you must test it. Diligent testing is the cornerstone of any effective treatment program. In this primer on test methods, we’ll explore the analytical methods commonly found in water test kits—color-matching, titrimetric, turbidimetric, and electronic—so you can choose the best one for your needs. Included throughout the discussion are testing tips to help maximize the accuracy of your results. For more information, see “Testing technique” below.
In a color-matching (colorimetric) test, chemical reagents are added to a water sample where they react with the analyte of interest (free or total chlorine, copper, ammonia, etc.) to produce a color proportional to its concentration. The color of this treated sample is then compared to a set of color standards until a match is made. There are several types of color comparators on the market. One contains printed-color standards, while a second holds liquid-color standards. A third type features colored-plastic standards. All three types require you to differentiate between colors—often hues in the same range, such as the shades of pink used in many chlorine tests—to determine chemical concentration.
To find the best color match, follow the instructions carefully. For example, some manufacturers may say to hold the color comparator at eye level with the sun off to your side (i.e., not shining directly through the comparator nor directly onto the faceplate) when testing outdoors. When testing indoor water features, it may be necessary to use a special lamp—not incandescent or fluorescent lighting—to simulate daylight for a proper color match.
Before ordering a colorimetric test, it’s important to determine the likelihood of encountering color or turbidity in your water samples since these factors will interfere with color-matching tests. For example, if you’re planning to analyze pH in colored pond or stream water or chlorine in cloudy, winterized pool water, you must either filter the sample prior to testing or choose a system that can compensate for the interference. Regardless of the type of color-matching system you choose, be sure to select a kit with color standards in your target range.
Testing Tips: Whenever testing outdoors, remove your sunglasses before making a reading because they will interfere with color perception. If you are among the 6%–8% of the population estimated to have red-green deficiencies in their color vision (mainly men), some colorimetric tests will be a problem for you. Be aware of your limitation and look for alternatives. For example, the color standards used with DPD chlorine tests are all shades of pink. If you have trouble differentiating between the hues, use an FAS-DPD titration test instead, or let a colorimeter read the sample for you.
Printed-color standards, by definition, cannot mimic the characteristics of an aqueous sample. Nevertheless, color cards and test strips are often used to measure sanitizer levels, water balance parameters, and metals in watershapes. Test strips are also available for testing water in living systems where parameters such as pH, alkalinity, hardness, ammonia, nitrite, and nitrate must be monitored to protect the health of plants and fish. In color card tests, you add reagents to a water sample, which will then develop a color. You compare the treated sample to printed-color standards corresponding to a range of concentrations and determine which standard most closely matches the sample’s color. When using test strips, you simply "dip and read," matching the color(s) that develops on the pad(s) against color standards that are usually affixed to the container. Be sure to follow the manufacturer's instructions regarding immersion time; whether to swish, swirl, or dunk to properly expose the reagent system to the water sample; and time to let elapse before taking your reading.
Test strips work well for quick checks of watershapes with well-known chemical requirements because they allow you to ensure water quality parameters are within the expected ranges. But, suppose for example you’re using a typical total alkalinity test strip (with printed-color standards for 0, 40, 80, 120, 180, and 240 ppm) when analyzing the water in a pool, and you get a reading between 40 and 80 ppm. How much sodium bicarbonate should you add to increase the alkalinity to 100 ppm? The simple answer is: You don’t know exactly. The test strip doesn’t provide the resolution necessary to translate test results to treatment, and you will likely underdose or overdose. In this example, it would be better to use a drop-count test that can provide a total alkalinity reading in increments of 10 ppm, allowing you to more accurately calculate the chemical dosage from a treatment table.
Testing Tip: With printed standards, important quality distinctions include how close the printing comes to the target colors (digital printing is superior to four-color printing), whether the manufacturer consistently achieves the same colors from press run to press run, and how the standards hold up under constant use in wet environments (lamination or waterproof paper helps).
Liquid-to-liquid color matching is more dependable than a liquid-to-nonliquid comparison, which is why many upper-end test kits feature liquid-color standards. In these tests, you add reagents to a water sample, which then develops a color proportional to the concentration of the analyte of interest. You then compare this color to multiple liquid-color standards housed in a handheld comparator, looking for the closest match. For example, a typical iron comparator might include standards for 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, and 2.0 in hues ranging from light to dark purple.
Testing Tip: The best liquid standards are guaranteed never to fade over the lifetime of the comparator.
Liquid-to-liquid comparators are extremely easy to use, portable, and available in the ranges most often encountered in watershapes. Exercise reasonable care (do not drop, leave out in the sun, or let freeze) and you will enjoy many years of service from a modest investment.
Many water-quality parameters—for example, alkalinity, bromine, chloride, chlorine, and hardness—can be monitored with a simple procedure called a titration. The first step is to collect a sample of the water to be analyzed and carefully measure it out according to the test instructions into a graduated sample tube or flask. Next, a special indicator is added. (The indicator will change color at a specific point in the reaction called the endpoint. This is the moment in the analysis when the test reading should be taken.) Finally, a reagent of known concentration, referred to as the titrant, is added incrementally until a permanent color change takes place. For example, in a total alkalinity test you would see the treated sample turn from green to an admixture of both green and red to all red at the endpoint. The concentration of the analyte of interest is calculated based on how much titrant was added. A white background is helpful to see the endpoint color change.
Generally, field test kits offer a specific type of titration called a drop-count titration or "drop test." Titrant is dispensed from a dropper bottle or pipet into a treated water sample until the endpoint color change occurs. They’re quite popular because they are portable, require minimal technique, can be performed in a minute or two even by inexperienced analysts, offer a degree of accuracy sufficient for most applications (this depends upon the quality of the dropper tip, but ±1 drop in 10 is common), and are very economical. In addition, there are usually few components, no calibration is required before use, and the upkeep on a kit is negligible. (Some manufacturers offer systems that use microburets for dispensing the titrant or "reverse titrations" in which the sample is added to the titrant until the endpoint is reached.)
Testing Tips: Be sure to hold the dropper bottle or pipet straight up and down when dispensing reagent to guarantee the proper drop size. If you notice the drop size becoming smaller, remove the static causing this by wiping around the tip of the bottle with a clean, damp paper towel. (Best bet for avoiding the possibility of contamination: Wet the towel with a few drops of the reagent you're using. If you use this approach, be sure to avoid personal contact with reagents containing any harmful substances.) Swirl after adding each drop to mix it into the sample thoroughly. When in doubt a permanent color change has occurred, add one more drop of titrant. If the color does not change any more, do not count this drop.
The turbidity of an untreated water sample can be used as a general indicator of water quality. Similarly, the turbidity of a treated water sample can be used to measure individual analytes such as cyanuric acid (CYA). In water sanitized with chlorine, CYA is often used to protect the free chlorine residual against degradation by sunlight. When conducting a turbidimetric test, reagents are added to a water sample where they react, causing a precipitate to develop. The turbidity of the solution is then analyzed by either visual comparison or use of an electronic meter.
Visual comparison generally involves viewing a marker through the sample; the degree to which the marker is obscured by cloudiness in the water correlates to the concentration of the analyte. For instance, one visual turbidity test for CYA, based on view depth, involves a printed black dot on the bottom of the test cell itself. While viewing the dot from above, you pour treated sample water into the cell until the dot is obscured, and then determine the concentration from calibration marks printed on the side of the cell. In a similar test, you fill a plunger-type test cell with sample water and add a reagent. You mix the sample for a short time to allow turbidity to develop and then look down through the sample while lowering a plunger with a black dot printed at its base. When the black dot is obscured you take a concentration reading from calibration marks printed on the plunger. In an electronic test, an instrument is used in place of the human eye to analyze the sample's turbidity, usually by measuring the degree to which light is refracted by particles in the sample.
When properly maintained and calibrated regularly, microprocessor-based instruments offer a high level of accuracy for field-testing. Handheld meters can be used to measure parameters such as pH, temperature, conductivity, resistivity, total dissolved solids (TDS), oxidation-reduction potential (ORP), and many other parameters of interest to those who test and treat water in watershapes. Some instruments measure one parameter, while others measure multiple. The best are built to withstand the demands of field-testing, boasting waterproof, dustproof, and chemical-resistant housing; ergonometric design; intuitive operation; preprogrammed methods for multiple analytes; automatic "housekeeping"; the ability to log your data and download it later to a PC or printer; and the potential for a certain amount of customization. Such meters enable even those with minimal technique and knowledge of water chemistry to be successful water analysts. Electronic controllers go one step further by continuously analyzing water quality parameters and activating water treatment and mechanical systems as needed to keep the values within a specific range.
While their use was once limited largely to a laboratory environment, portable colorimeters and spectrophotometers are also beginning to see greater use in field-testing. The technology employed in these units makes them far more sensitive to light and color than the human eye, and they analyze samples in the same way each and every time for repeatable results. Together, these characteristics make the devices very accurate and precise. The basic premise is this: Light is passed through a prepared water sample and onto a detector that measures the amount transmitted through (or absorbed by) the treated sample. Light of different wavelengths may be used depending upon the parameter being analyzed. The measurement of transmitted or absorbed light is then converted to a reading of concentration by software in the meter. These instruments are a good choice when you need to monitor a parameter at ultra-low levels.
But, electronic instruments are not yet a replacement for all other methods. Their price can be prohibitive to many when the wet chemistry tests discussed above can do the job. They require more care. They can be out of commission most inconveniently, although service loaners are sometimes available for a fee. And, just as with their PC cousins, the minute you invest in one somebody introduces something better! Still, no one can afford to ignore the benefits instrument manufacturers have made available to those testing water today.
Testing Tip: Investigate the availability of calibration standards, pH buffers, DI water, etc., from other sources besides the meter manufacturer. It may be less expensive to buy the "blades" for your "razor" elsewhere, particularly if the warranty period has passed—though, admittedly, finding compatible reagent systems for these devices can be problematic.
While the preceding survey is by no means exhaustive, we hope you've gained some insights that will prove helpful in the start-up and ongoing maintenance of your watershapes' chemistry. By understanding the testing options available, you can choose the best one for a given application, thereby ensuring accurate test results, an effective treatment program, and, ultimately, satisfied clients.
Test results are, to some degree, a function of testing technique. To obtain the most accurate readings possible, follow these guidelines:
- Prior to testing, be sure your hands and work area are as clean and dry as possible. Also, keep a notepad or logbook nearby to record test results.
- Familiarize yourself with test instructions before beginning a test—especially when running a test that's new to you—and follow them exactly. Note any special considerations stated in the instructions such as required wait times, safety warnings, and conversion factors for test results.
- Before beginning, make sure you have the reagents and labware necessary to perform the test, and verify all components are in good condition.
- For meaningful test results, take a water sample representative of conditions in the whole system.
- Before gathering a sample, always rinse the test cell with the water to be tested to prevent contamination from any residue. This is especially important when using the same test cell to analyze multiple parameters or when using equipment at multiple testing locations.
- When gathering a sample for off-site analysis, such as at a pool/spa or pond supplies store, fill the container to overflowing and cap it so no air is present.
- With on-site analyses, test immediately after sampling, since some values (halogen sanitizers in particular) can change within minutes.
- After testing, flush out the test cell with demineralized water, and wipe equipment down with a clean, dry cloth.
- To prevent contamination of reagents, don't interchange container caps and always replace them securely.
- For the same reason, never cap a sample container with your finger while testing.
- If exchanging one manufacturer's reagents with another's, be sure they're equivalent strength.