Langelier Saturation Index

In my service area, the water supply has moderate calcium hardness in the supply water and I am able to change water if water hardness is above 600 ppm. Therefore, I have not used or needed the Langelier, the Hamilton Theory, or any others. I know when water is corrosive or when it has scaling tendencies. So by keeping this in mind and testing water hardness occasionally, I do not need to use these complex systems. But in areas with high calcium hardness in the supply water (ours is around 250 ppm), using these formulas may be the way to go if you use all the variables and modifications needed to do this properly.

Dr. Langelier used this method many years ago to calculate a safe saturation point at which to maintain water. But this was originally for water in a closed, confined environment. Pool water is open and exposed to the air and this can be a different ball game. TDS was not included in original theories and several modifications have been added through the years to compensate for the difference in confined and closed water properties. This is too complex for me; but if I needed to use the Langelier theories, I suppose I could stagger through them. If you can follow my recommendations as to where to maintain water hardness, TA and TDS and stick with these ranges, in most instances you will not need complex formulas.

One consideration that must be acknowledged is water temperature. As temperatures change, this formula must be – re evaluated accordingly – which seems to me very time consuming. I allow a year-round average for my water and maintain ranges of pH and total alkalinity corresponding with water hardness and have been lucky so far. But in water that is heated most of the time, high in calcium content, of for maintaining commercial pools ( where health codes require saturation balances to correspond with the Langelier Index), then consider learning and using this method. But if you don’t need it, why spend the time using this method?

Different strokes for different folks. What the Ph.D. boys call the saturation point or balance, I call a buffer zone. Regardless of how we arrive at the ranges for safe, buffered water, getting there is an important part. I compared and overall balance range of my services and used average year-round temperature to compare my method and theirs, and I was right in the same area. I do not like to be technical, as I don’t have the necessary background or education, but I will give it my best shot.
Water hardness is referred to as the calcium factor (CF), total alkalinity is referred to as the alkalinity factor (AF) and temperature of water (TF), and use the pH factor of the water tested. Substituting actual numbers from my service, CF= 300 ppm; AF= 120; average TF= 66?and pH= 7.6. Add these and subtract the constant 12.1:

CF=2.1
AF=2.1
AF=2.1
TF=0.5
Ph=7.6
=12.3
(-)12.1
=0.3

According to their calculations, I am as close as the original conclusions without using any modification- if within 0.3 plus or minus water was in the acceptable saturation range.

Langelier Numerical Equivalents Table and Equation Theory Chart (Temperature= TF; Total Alkalinity= AF; Calcium Hardness= CF; and pH Factor)

Test pH, add to TF + AF + CF, and subtract the constant 12.1