Testing solutions for water studies.

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Testing solutions for water studies.

When and how to test.

Some significant changes can take place in a water sample after it has been collected. Carbon dioxide and oxygen levels can change and this can affect pH and solubility of some metals like iron.

Samples taken at different locations along a creek or river can help identify sources of pollution. However in lakes and dams many water factors change with depth so that needs to be considered when making interpretations.

Some studies compare samples taken at different times at the same location. This can be a very useful approach to help understand the processes that are at work in the water. Keep in mind that some factors change daily in natural waters, for example if there are large numbers of algae present.

Another approach is to study the effect of some treatment on duplicates of the same sample. An example would be a study of exposure to sunlight or UV light on bacterial growth and survival. These types of studies are challenging because it is very difficult to minimize the effect of all other factors. It is also difficult to apply or interpret the results in real situations.

 

Salts.

The total amount of salt in water can be easily estimated using a conductivity tester. The conversion between conductivity and salts as Total Dissolved Salts in ppm is approximate but it can still give a convenient estimate. Many conductivity testers can also show TDS in ppm by using their TDS factor. Some of the budget tests have a set TDS factor but with others the user can set the TDS factor. TDS is useful for comparing measurements against published or existing TDS values or values for individual components like salts. A simple conductivity measurement is all that is needed for a quick comparison between samples / locations. All conductivity testers need to be calibrated with a calibration solution. The instructions for each tester will indicate which standard solution is required. Testers such as the Hanna Instruments DiST 5 test in the range most useful for testing drinking and process water. The DiST 5 is waterproof and calibration is menu driven. These two factors alone are very important if using the tester in the field. The DiST5 also shows temperature so it can be used as a thermometer.

Conductivity can't be used to distinguish between the different salts. The main salts to consider are sodium, chloride, calcium and magnesium. The last two calcium and magnesium can be roughly estimated by hardness.

Hardness.

Hardness can be measured by test strips and test kits. Hach hardness test strips measure from 0 - 425 ppm as Calcium carbonate. See details at Hach hardness test strips. For greater accuracy there is a test kit made by Hanna Instruments the HI3812 hardness kit. The sample size can be varied to allow for higher resolution at low values. See details at HI3812 hardness kit.

ORP.

Oxidation Reduction Potential (ORP) or REDOX is measured with an electronic ORP tester. There are testers that measure only ORP such as the HI98120 ORP / temperature tester. See details at HI98120 ORP / temp tester. All ORP testers need a calibration solution. It is possible to buy a combination ORP / pH tester. This is a cost effective solution as pH and ORP are frequently measured together. A good example is the Hanna Instruments HI98121 ORP / pH tester. See details at HI98121 Combo ORP / pH tester.

Dissolved oxygen.

For lower level classes choose the TesTabs Lamotte Dissolved Oxygen TesTabs method Code 5889. The TesTabs methods are safe and convenient for students in lower grades. Dissolved oxygen TesTabs measure 0, 4.0 and 8.0 ppm oxygen. See details of kits that are built on the TesTabs system at Lamotte Green Low Cost water monitoring kit. For more accurate and wider range oxygen measurements a test kit is needed. A good example is the Hanna Instruments HI3810 Dissolved oxygen kit. See details at HI3810 Dissolved oxygen kit. Although there are several steps involved, all reagents are dispensed easily with dropper bottles. The kit uses a Modified Winkler procedure and includes a simple titration.

Carbon dioxide.

Testing for carbon dioxide is really a test for that proportion of carbon dioxide in water that has dissociated in water to form carbonic acid. In some ways it is a test for acidity in water because the usual test method is a titration to neutralize the acidity. Test kits usually give the result as ppm of carbon dioxide. A good example is the Hanna Instruments HI3818 carbon dioxide kit. See details at HI3818 carbon dioxide kit. Titrations are more suitable for students at upper levels.

pH.

The two main methods for pH testing are pH test strips and electronic pH testers. Test strips are best for routine screening tests. The smallest step size is around 0.5 pH units for test strips with a range suitable for most natural waters. A good example is Macherey Nagel pH-Fix test strips with range 4.5 - 10. See details at pH-Fix test strips 4.5 - 10. There are several electronic pH testers available. For outdoor and field use waterproof testers that have menu driven calibration are much easier and convenient to use. For a stand alone pH tester see pHep 4 pH tester. Some pH testers are combined with either ORP or conductivity and this may be a more cost effective solution.

Ammonia.

Ammonia in water can be tested with test strips or with a test kit. For students at lower grade levels Hach ammonia test strips are convenient and easy. See them at Hach Aquachek ammonia test strips. These test in the low 0 - 6 ppm range which is the range appropriate for most natural waters. The test strips show ammonia - nitrogen. For upper grade levels the Hanna Instruments HI3824 ammonia-N colorimetric kit is a good introduction to test kits. It tests ammonia - N in the range 0.0 - 2.5 ppm. (The saltwater version is HI3826). It is important to measure pH along with ammonia measurements. In water, ammonia if present is in balance with ammonium ions. In acidic (less than pH 7) solutions less harmful ammonium dominates but as pH rises harmful ammonia levels increase.

Nitrate / nitrite.

Hach Aquachek nitrate / nitrite test strips test both nitrate- nitrogen and nitrite - nitrogen on the one strip. The range of both will cover from low values found in natural waters to higher values typical of contaminated waters. See them at Hach Aquachek nitrate / nitrite test strips. Hach test strips are suitable for students in lower grade levels.

For students at mid to upper levels the The Macherey Nagel Visocolor ECO nitrate test kit 931041 offers an introduction to photometer methods. The kit can be purchased as a visual kit with colour chart or as a refill kit that can be read by the Macherey Nagel PF-12 photometer. The kit measures nitrate over a wide range. See details of the kit at Macherey Nagel Visocolor nitrate test kit.

For extended testing of a wider range of factors teachers should consider instrument methods. One example is the Macherey Nagel PF-12 photometer system. The photometer is pre programmed to read reaction colours from approx 100 test kits for water analysis. The advantage is rapid, objective and accurate readings. See details of the kit at Macherey Nagel PF-12 photometer.

Phosphate.

For all students particularly those in lower grades there is an easy solution for testing phosphate. The Lamotte phosphate test strips Code 3021-H test phosphate in the range 0 - 2.5 ppm as PO4 in steps 0, 0.1, 0.2, 0.3, 0.5, 1.0 and 2.5 ppm. In most natural waters phosphate levels range from 0 to around 2.5-3.0 ppm. Higher phosphate levels, up to around 5 ppm are often found in recycled water, greywater and agricultural runoff water. To measure these higher levels dilute the sample with distilled water then test using the Lamotte test strips. Remember to multiply the reading by the dilution factor.

The disadvantage of test strips is that resolution of intermediate values can be difficult. The Macherey Nagel Visocolor HE phosphate kit tests phosphorus (multiply by approx 3.1 to get phosphate) to 3 mg/L in 9 steps. This kit uses a colour wheel and comparator that incorporates a sample blank. In this way compensation is automatically made for the colour of the sample. Code is 920082. See details at Macherey Nagel Visocolor HE phosphate kit.

For wide range phoshate testing that includes waters with high nutrient loads choose the Macherey Nagel Visocolor ECO phosphate kit. This kit measures phosphate - P in the range 0 - 5 mg/L in 8 steps. This kit can also be used with the PF-12 photometer. If the photometer is to be used then only the reagent set for the kit has to be purchased. See details of this kit at Macherey Nagel Visocolor ECO phosphate kit.

Turbidity.

We're currently looking into Turbidity tests so, watch this space.

Bacteria.

These are easy to use for students, are quantitative and reliable. The two basic types are Coliscan Easygel for E coli and coliforms together, Total count Easygel for aerobic plate count. These are the groups used in the Australian Drinking Water Guidelines as indicators of water quality. Each kit has 4 parts, 1 treated incubation plate, sterile sample bottle, sterile dropper and Easygel media. Once a small sample is added to the media bottle it can be poured directly into the dish. The media sets after about 1 hr so there is no preparation involved and no hot growth media to prepare. The tests give actual counts per 100 mls of sample. Results are reported as Colony Forming Units / 100 mls. This is a standard way of reporting and can be used for comparisons against samples from other studies. On the Coliscan plates, E coli and coliforms are distinguished by their colours and are counted separately. Counting is easiest using a hand magnifier and a 1 cm x 1 cm grid on an acetate sheet. Instructions are on the Apps labs website. There are many pages on the Apps Labs website describing the Easygel tests. Start at bacteria testing in the classroom.

 

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