Pool/Spa Water Care
Is Pool Water Potable?
By Dietitian,
February 21, 2010 in Hot Tub Water Chemistry
The point of pool water maintenance is to disinfect/protect from pathogens, but also to protect our spas from corrosion and calcium deposits. With this in mind, Evian Water, when measured with a Taylor kit, indicates the following:
TA: 340
CH: 240
FC: 0
CC: 0
PH: 7.2 (Actual listed on bottle: 7.18)
This yields a CSI of 0.08, which may be close to 0.00 with 7.18 PH.
City water has the following stats:
PH 8.6+
TA: 90
CH: 90
CSI: 0.60
Would this indicate that my hot tub water is not only safe to drink, but is less corrosive / calcifying for my teeth than city water?
chem geek
Location:San Rafael, CA
Interests:Interested in pool water chemistry. Undergrad degree in physics/chemistry. MBA. Other interests include swimming, skiing, genealogy.
Because of disinfection by-products, your hot tub water (or pool water) is not considered to be safe to drink. Even without the disinfection by-products, the buildup of chloride (salt) would be too high for daily consumption unless you were to eliminate salt from all other parts of your d-i-e-t (for some reason, writing this word without dashes turns it into *** perhaps as some sort of spam trigger). In an emergency, such as an earthquake, a good source of drinking water is from a hot water heater.
Your teeth are more affected by pH and do not require calcium carbonate saturation -- they are not made of calcium carbonate. The calcium matrix of bone and teeth is different than calcium carbonate.
The Evian water is over-carbonated more than usual -- a higher TA and lower pH. Your city water is more typical except that the pH is unusually high -- normally it's around 7.7 to 8.2.
What does "over-carbonated" mean?
Over-carbonated means that there is more carbon dioxide in the water than would be naturally in the water based on exposure to carbon dioxide that is in the air. A carbonated beverage is an extreme example. The Evian may be over-carbonated since it comes from spring water dissolving calcium carbonate in rock and not being exposed much to the air. Over-carbonated is not bad. It just means that the water will tend to rise in pH with aeration, stirring, etc.
Over-carbonated means that there is more carbon dioxide in the water than would be naturally in the water based on exposure to carbon dioxide that is in the air. A carbonated beverage is an extreme example. The Evian may be over-carbonated since it comes from spring water dissolving calcium carbonate in rock and not being exposed much to the air.
Would boiling the Evian water remove C02 and raise the PH?
Just stirring vigorously or blowing bubbles through a straw would probably accomplish that. However, there isn't much reason to do that unless you were worried about the lower pH. 7.2 isn't that low -- it's still slightly alkaline. 7.0 is neutral. Note that all that will happen is the pH will rise; the TA and CH and other parameters will stay the same. The CSI will increase, but it's doubtful that it will be enough to have scaling (unless you got the pH much closer to 8.0).
Yeah I don't necessarily want to raise the PH of the water, but I was curious about how sensitive it would be to C02 loss....
Our blood, eyes, and mucus membranes are PH 7.4 as I understand it, so I would imagine that finding a water with PH 7.4 would be ideal, no?
A pH near 7.5 is close to tears and bodily fluids. As to whether this is ideal for drinking water, there is a lot of debate on that, mostly by some unscrupulous folks promoting alkaline diets and the like. Basically, it's better to have something at least a little alkaline in order to prevent acidity that can cause tooth decay. Tap water that often comes closer to 8.0 or even 8.5 is fine. Note that carbonated beverages can be very acidic with some that have a pH of 3 or lower.
Pool Clown
Location:Silicon Valley, CA
Usually, when i read Richards posts, I can only hang on for a little while then what is written turns in to another language, and i loose him. But i made it thru this one. I think i get it.
The World Health Org. standard is:
Total dissolved solids (TDS): Min 100ppm, ideal is 200-400ppm
PH (Acidity): As close to 7 (Neutral) as possible
Calcium: Min 20ppm, ideal is 40-80ppm
Magnesium: Min 10ppm, ideal is 20-30ppm
http://www.who.int/water_sanitation_health...mineralized.pdf
Their recommendation for PH 7 seems a little strange if our teeth begin to dissolve at 5.5, our tears are 7.5, and our blood is 7.4:
"The mean pH values of 40 eyes from 20 healthy volunteers was 7.50 (SD +/- 0.23)"
"the mean pH value for the six subjects [tears] was 7.50 ±0.16 (SD)"
http://www.iovs.org/cgi/reprint/30/4/747.pdf
"Blood pH is regulated to stay within the narrow range of 7.35 to 7.45"
http://en.wikipedia.org/wiki/Blood#pH
quantumchromodynamics
You have to remember that the water we drink goes into our stomachs where the pH is already low due to the hydrochloric acid in the stomach.
Tooth enamel does not decalcify in acidic solutions unless the pH is below 6.0 (6).
(6)McClelland JR. The decalcification of human tooth enamel. Dental Cosmos 1926;68:127-32.
Pool water or drinking water can cause dental corrosion if the pH is too low.
Ca10(PO4)6(OH)2 + 8H+ --> 10Ca2+ + 6HPO42- + 2H2O
Most I.V fluids are acidic at a pH from 3.5 to 6.2.
Pool water is maintained around PH 7.5, so it should be ideal for avoiding irritation to skin and eyes; and I would imagine that drinking water PH should ideally be similar to pool water.
From the link about IV fluids: "The acidity of [i.V] fluids has been criticized for its corrosive effect on veins." It is acidic to keep the fluid stable in the bag, but it damages veins.
The article about acidic pool water is amazing; the maintenance guy tested the water at PH "6.8" but that is the bottom of the range for the red phenol drop test, additionally, he failed to keep records of the testing, so he likely didn't do anything to the water at all (it had an automatic gas chlorination system), and it was allowed to reach a PH of 2.7!
I think the dental erosion issue brings up an interesting point. Namely, what pool water chemistry conditions can cause dental erosion? I know that low pH is going to be the most important factor.
I think that an extremely low CSI levels could contribute to dental erosion in swimmers who spend a lot of time in the water and allow a lot of contact time between the water and their teeth.
Whether or not dental enamel is eroded by the water can be determined from the solubility product of carbonated hydroxyapatite.
Carbonate ions can substitute for the hydroxyl groups (Type A), or the phosphate groups Type B.
In addition to maintaining an adequate pH at all times, I think that people should avoid very low CSI levels just in case low CSI has an adverse effect on teeth.
There have been several well documented cases of swimmers who have had severe dental erosion due to aggressive pool water.
I think that only severe cases have been traced back to swimming pool water. I think that there have probably been many cases where minor to moderate erosion has occurred due to swimming pool water, and in most such cases, the swimming pool water would not have been identified as the cause.
A low CSI means waster is "calcium hungry" and would be able to pull calcium from the enamel (hydroxyapatite). Is this correct?
The saturation index tells you if the water is saturated with calcium carbonate so whether it will tend to scale or dissolve calcium carbonate. That is not the same thing as whether it will tend to dissolve other calcium compounds. In that case, it would be the Calcium Hardness (CH), that is the calcium level, that would be more relevant, but how much I couldn't say. I suspect that pH is far more relevant. This link seems to bear this out. Calcium and phosphate levels in saliva are at 1.5 mMoles/liter which for calcium represents a Calcium Hardness (CH) of 150 ppm and around 142 ppm phosphate which is a very high phosphate level (it's 142,000 ppb) compared to pools and spas. Other studies like this one show different calcium and phosphate levels, but still very high in phosphates.
Though technically drinking water that is lower in CH, say 50 ppm, and very low in phosphates, say 50 ppb, would have a much lower ion product, at normal pH of at least 7 the product of concentrations is still far, far higher than the solubility product, meaning that normal tap water does not tend to dissolve tooth material. Carbonated beverages, on the other hand, are a much bigger problem due to their low pH.
The hydroxyapatite is actually "carbonated hydroxyapatite".
Therefore, calcium and carbonate will both be relevant.
Carbonated beverages are especially problematic beyond what you would expect just from the pH due to the way carbon dioxide reacts with calcium carbonate, the hydroxyl group and the phosphate group.
CO2 + CaCO3 + H2O --> Ca2+ + 2HCO3-
CO2 + OH- --> HCO3-
CO2 + PO43- + H2O --> HPO42- + HCO3-
From a dental perspective, the most important contaminant is carbonate which has a major effect on increasing apatite solubility. Reference
Structures of the apatites in enamel, dentine and bone
Even with carbonate being able to substitute for phosphate, that does not mean that saturation of calcium carbonate is needed. The Ksp for the tooth material is far, far smaller than that of calcium carbonate and as I referenced in my earlier post, even 50 ppm calcium hardness with 50 ppb phosphates at a pH of 7.0 has a product of concentrations (with hydroxyl ion) that is far, far higher than the Ksp. So unless the Ksp for the tooth material when carbonate is used instead of phosphate is far, far higher, then saturation with calcium carbonate is not necessary.
So unless the Ksp for the tooth material when carbonate is used instead of phosphate is far, far higher, then saturation with calcium carbonate is not necessary.
The reference does state that carbonated hydroxyapatite is much more soluble than non-carbonated hydroxyapatite, although it doe not give the Ksp.
"Biological apatite composition varies so widely that any measure of solubility product is largely meaningless. It is, however, generally accepted to be very much more soluble than hydroxyapatite."
From a dental perspective, the most important contaminant is carbonate which has a major effect on increasing apatite solubility.
Do you agree that carbonated beverages are more risky than just the low pH?
Since the water is supersaturated with carbon dioxide, the carbon dioxide acts as a source of Total Acidity.
Normally, when the hydrogen ions dissolve calcium carbonate, the pH will rise and the solution will become less aggressive.
However, the carbon dioxide will prevent the pH rise because it will create more hydrogen ions as the ions in solution get used up.
This creates a solution that has a larger total capacity to dissolve calcium carbonate.
Does this still indicate that teeth are more damaged by carbonated beverages, even though teeth are not made of calcium carbonate?
Does carbonation affect the water's ability to dissolve the tooth's hydroxyapatite (crystalline calcium phosphate) material ?
I think that the primary risk is from the low pH.
Tooth enamel is made from "carbonated hydroxyapatite" which contains calcium, carbonate, phosphate and hydroxide.
I think that the levels of calcium, carbonate and phosphate are a distant second to pH as far as solubility is concerned. I don't think that carbonate levels will be a concern in a pool that is maintaining an adequate pH.
I think that calcium levels should not be left under 100 ppm, just to be safe. I really don't know if it is a real risk or not. I don't think that there would be many cases where the calcium level would be near zero, but it could happen.
If the teeth are exposed to fluoride, the fluoride will substitute for some of the hydroxyl groups and form a more stable compound called fluorapatite.
The carbon dioxide acts as a source of Total Acidity, which reduces the amount of pH rise that would otherwise occur as the hydrogen ions began to combine with other elements. This gives the water a greater total capacity to dissolve the tooth enamel.
This is also dependant upon the total length of time that the teeth are exposed to the carbonated water and upon the total amount of water. If the time is brief, then the carbonated water should not be substantially more corrosive than non-carbonated water that had the same pH.
If the volume of water is large compared to the material being dissolved then the carbonated water should not be substantially more corrosive than non-carbonated water that had the same pH
Total Acidity is similar to Total Alkalinity, but it measures resistance to pH rise, whereas Total Alkalinity measures resistance to pH drop. Total Acidity is measured using a base as the titrating agent instead of an acid.
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