Water studies - get involved!

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Water studies - get involved!

With the number of possible tests that can be done on water its tricky to know where to start. So choose tests that answer a question or help explain how the water has got to its current condition.

- Can the water be used for irrigation? The key factor is the amount of dissolved salt in the water. Other important factors are the salts made up by chloride, sodium, calcium and magnesium.

- Can the water be used for drinking? Slightly difficult to answer because that would require testing a large number of factors including contaminants like metals and chemicals. But there are a number of 'quality' indicators that can be measured. Factors like pH, redox potential, dissolved oxygen, organic matter loading, carbon dioxide, bacteria levels and turbidity can indicate that there is an underlying problem for example, some type of contamination. Water that is relatively 'healthy' is easier to treat to make it suitable for drinking. There are also 'risk' factors that also need to be considered for example is there any risk of industrial or agricultural chemicals entering a water supply. Testing 'quality' factors can lead to a better understanding of how the water can be managed or treated.

- Can the water be used for industrial purposes including food processing? Key factors are salt content, dissolved metals and hardness. Again, water 'quality' factors are important.

- Is the water suitable for fish and wildlife? Again a wide range of specific chemicals and contaminants may be present but pH, redox and turbidity are critical starting factors because they can indicate underlying problems. For example a common source of contamination in natural water is organic matter. This can increase carbon dioxide and ammonia and deplete oxygen. Therefore these factors can be used as indicators of organic pollution

Dissolved salts.

Salts in water are important to measure because they can broadly indicate environmental changes due to salting and contamination from industrial processes. Salt level can influence species composition of plants and animals in the water and can effect plant growth if the water is used for irrigation.

Salts in water can be estimated using conductivity. However conductivity measurements can't distinguish between more undesirable salts like sodium and chloride and other less harmful salts like calcium, magnesium, potassium, bicarbonate and sulphate. Even more important for irrigators is the balance between sodium and the plant nutrients calcium and magnesium. If there is too much sodium both soil structure and nutrient availability may be affected. The calculated ratio is the same as used in soils, the sodium adsorption ratio.

Hardness in water is the term used to describe the amount of calcium and magnesium in water.

Dissolved gases

Carbon dioxide and oxygen are the most important ones. Carbon dioxide has a very important role in the pH of the water. Quite often a high carbon dioxide level results in low pH. This is because a small proportion of dissolved carbon dioxide makes carbonic acid, decreasing the pH. This can happen when water comes from underground where there is limited gas exchange or when water is contaminated by organic matter. Heterotrophic organisms break down the organic matter resulting in release of higher than normal levels of carbon dioxide. However interpreting carbon dioxide levels is challenging because other factors may be involved. For example because high levels of algae can use up much of the carbon dioxide during the day because of photosynthesis. Around 3 - 5 ppm carbon dioxide is normal for unpolluted surface waters.

Dissolved oxygen is critical for many aquatic organisms particularly fish. Levels of around 8 - 10 ppm are desirable whilst 3 ppm oxygen is too low to support many species.

pH and ORP.

If there were only two measurements that could be taken in water to assess that water's health they would be pH and ORP. The reason is relatively simple. Almost all major and important chemical and biological processes that occur in water are either directly influenced by, or conversely alter the pH and ORP. pH is the concentration of hydrogen ions and ORP (sometimes called REDOX) is an indication of the oxidizing potential of the water. If all of these processes are relatively well balanced or 'behaved' then the pH and ORP values for your water should fall within acceptable limits for that water type. For a more detailed explanation of these two factors see pH and ORP in water. Because oxygen is the most significant oxidizer in water he amount of oxygen strongly influences ORP, keeping it in the positive range around 250 - 400 milliVolts. Oxidation reactions tend to keep water clean and fresh whilst reduction reactions tend to create chemical products that have unpleasant smells like ammonia and sulphides. pH also plays a part in oxidation reduction reactions. Low pH helps to create those unpleasant smells and to make dissolved metals like iron more soluble. Fresh smelling clean water tends to have a higher pH.

Turbidity.

Turbidity is a general measurement that indicates cloudiness in water. It is mostly caused by colloids, very small charged particles composed of combinations of clays and organic matter that stay suspended in water. High densities of algae and bacteria and very fine semi suspended organic particles can also make water look more turbid. Turbidity measurements can often be a useful indicator of pollution or contamination. Turbidity is an important factor because it reduces the amount of light entering the water. Low light reduces the number of photosynthesizing organisms that produce oxygen and use up carbon dioxide. This can start a chain of events that can eventually lead to degraded, low oxygen conditions.

Organic matter.

Organic matter in water can come from different sources and can be dissolved in the water or held in a semi-suspended form sometimes associated with minerals like clay particles. Some organic matter in water can be considered natural, like some humic materials. Other organic material can be from pollutants like manures, food wastes and greywater. An oversupply of organic matter can cause oxygen depletion in water and this can have a significant effect on animal life.

Nitrate, nitrite and ammonia.

These factors usually go hand in hand and they will tell a lot about oxygenation and organic load. Ammonia is very undesirable in water and can be toxic to organisms including fish. It usually occurs when organic matter containing nitrogenous material decomposes under low oxygen conditions. In well aerated water ammonia should not accumulate. Formation of nitrites is an intermediate step in the process that converts ammonium to nitrate. Normally nitrites are oxidized to less harmful nitrates in water if there is adequate oxygen. But if there is too much nitrogenous waste to break down the process may not have enough oxygen and nitrites will accumulate. Therefore presence of ammonia or nitrites indicates either organic matter overload or low oxygen or both. Nitrate levels are usually low in natural waters therefore the presence of high nitrates usually indicates pollution from organic matter or other forms of nitrate.

Phosphate.

In natural waters there should be low levels of phosphate. Therefore elevated levels are usually considered an indicator of pollution. Phosphate is a major plant nutrient and is the main factor implicated in excessive algal growth.

Bacteria.

Levels of bacteria in water are usually a good indicator of contamination. At Apps Laboratories we have established baseline figures for the three groups that are used by the Australian Drinking Water Guidelines. See What do your water test results mean. These are E coli, coliforms and total aerobic bacteria.

Where to next?

At Apps Laboratories we've put together a summary of safe, easy and affordable test kits that students can use at school and at home to start their water studies. See details at Testing solutions for water studies.

Further reading.

At Apps Laboratories we studied a farm dam in Central Victoria that was filled by waste water from a food processing factory. Read about the results we found at Water quality indicators.

For a more detailed discussion of factors usually tested in waters see What do your water test results mean.

Why pH and ORP are important Test these first!

 

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