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Corrosive or fouling water?

All water can be corrosive, scaling or balanced, regardless of whether it is potable. When it is corrosive, it affects the most easily oxidizable metals, such as galvanized steel or copper. Its tendency to corrode or scale depends on the type and quantity of inorganic compounds dissolved in it. One of the first characteristics that we should know about the water we receive at home or in the company is this tendency.
We must not lose sight of the fact that we are not referring to a health issue, but rather to an issue of the impact on the pipes and water treatment equipment.
There are five parameters that determine the trend of a water: pH, total hardness, total alkalinity, total dissolved solids and temperature.
The pH measures the concentration of acids that dissociate when dissolved in water. It can have values between 0 and 14. A pH of 7 means neutrality. A pH less than 7 corresponds to acidic water, and a pH greater than 7 corresponds to alkaline water. The lower the pH, the more acidic the water, and therefore the more corrosive. Vice versa, the higher the pH, the more incrusting the water.
Hardness is a measure of the concentration of dissolved calcium and magnesium in water. These cations tend to scale more than any other, so the higher the hardness, the greater the scaling tendency of a water.
Total alkalinity is a measure of the concentration of carbonates, bicarbonates and hydroxides in water. All of these tend to scale, so water with a high total alkalinity tends to be scaling.
Total dissolved solids and temperature increase the corrosive or fouling tendency given by the combination of the above parameters (pH, hardness and alkalinity).
One of the most commonly used indices to determine the corrosive or scaling tendency of a water is the Langelier Saturation Index (LSI). When this has values between -0.5 and 0.5, the water is balanced (the best state of equilibrium occurs when the ISL is 0.0). When the ISL is greater than 0.5, the water is very fouling, and when the ISL is less than -0.5, it is very corrosive. In the latter two cases, it is necessary to correct the tendency of the water. This can be done in several ways (adding an acid or an alkali, softening, osmotizing, dealkalizing...).
Balanced water is best, but what most affects the treatment equipment is fouling water. This is because the internal parts of the equipment (activated carbon, ion exchange resins, reverse osmosis membranes, quartz tubes of UV lamps, etc.) become encrusted and lose their capacity to treat water.
When a water softener is installed, it is common for the water to become corrosive. Therefore, before doing so, it is necessary to consult a water technician to avoid this condition.
From all this, before anything else, it is necessary to determine the ISL of the water, to know if it has a tendency to corrode or scale, and, if so, to act accordingly.

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