Know what’s in fill water before it enters the pool

By Scott Webb
March 24, 2008 8:30 AM
As another spring creeps up from the South, many pools across the nation will be adding water — filling or topping off. And whether a new pool is receiving its entire complement, or just a top-off to bring a winterized pool up to active service level, understanding source water is important.For with a spring fill, the hidden ingredients in source water become part of a pool’s chemistry just the same as if they’d been measured out and added from a big white bucket. Knowing what’s going into the pool along with the water — and how to keep it from making trouble all summer — is a matter of sound, fundamental pool care.


Waterborne Suspects

Unless a pool is receiving pure H2O from a large distilling plant, there will be quite a few passengers riding along with it. The most troubling of these are minerals, nutrients, metals and perhaps bacteria. Each has an effect on pool chemistry and health.
Hard water: The somewhat misleading descriptor “hard” means that water has a high mineral content. The minerals that most concern the pool professional are calcium and magnesium. Concentrations of either one of these change the feel of pool water on the skin, and can precipitate out in the pool, clogging filters and causing cloudy water and poor circulation. Often they will show up on surfaces in a thin white layer well designed to make such surfaces look old and unattractive. If adhered to a piece of the pool equipment such as a heater element — the likeliest place to find it — calcium scale can interfere with its function.Calcium drops out of solution onto heaters because, contrary to the general guidelines of the natural world, the warmer the water (and the water around the heater is very warm), the less soluble calcium is. Calcium is unusual that way — a freak, if you will. Most materials on earth dissolve more easily as water temperature goes up, but it takes all kinds.

Las Vegas Valley Water District <<>>

Hard Water Water is considered “hard” when it contains a high level of dissolved minerals. In the Las Vegas Valley, the two nontoxic minerals that cause our hard water are calcium and magnesium. They’re carried into Lake Mead from the mineral-dense Colorado River and do not pose a health risk. The hardness of Las Vegas Valley Water District water is about 298 parts per million (ppm) or 17.4 grains per gallon, categorized as “very hard.”

The water in Lake Mead, which represents about 90 percent of our water supply, begins as snowmelt in the Rocky Mountains. As it makes its way to the Colorado River channel, it dissolves minerals such as calcium and magnesium from the surrounding rock. While these minerals pose no health risk, the residue can be a nuisance.

<NOTE:  This portion of article was added for those residents of Las Vegas, NV>

Soft water: Soft, being the opposite of hard, indicates water that is low in minerals such as calcium and magnesium. All things seeking balance in the world, water bereft of calcium goes looking for it in the plaster, degrading its appearance in the process.

Naturally soft water comes from rain, rivers, lakes and snowmelt, and tends to have a low pH. Such acidic water is hungry for metal parts in the plumbing, which it eats and eventually leaves corroded and useless.

Artificially softened water has been put through a process familiar to many households, where calcium and magnesium ions are replaced by sodium ions in a large, in-line tank. The difference between natural and artificial soft water is that the latter has a neutral or alkaline pH and therefore does not tend to corrode surfaces. It also has a higher TDS level.

Nutrient-rich water: Organic compounds such as phosphates and nitrates can be present in source water from lakes and rivers, and these carbon-hydrogen chains are like hot dogs and hamburgers to the tiny creatures known as algae.

In the presence of sunlight, lolling in warm water, all types of algae will eat organic matter and reproduce rapidly, if they can find a place in the pool not well-sanitized. Whether black, green or mustard-colored, a large colony of reproducing algae is a huge turnoff for bathers.

Another more recent and growing problem caused by phosphates is their effect on salt chlorine generators. High levels of phosphates in the water have been found to coat the metal plates in such systems, preventing them from producing enough chlorine to sanitize the pool.

This situation, the combination of low chlorine levels with a veritable smorgasbord of phosphates, is an algae population explosion waiting to happen.

Metal-rich water: The metals most often cited for trouble in the pool are copper, iron and manganese, and all of these can be present in any water source, municipal or private. Like calcium and magnesium, these metals can suddenly fall out of a clear water solution, turning the water green or brown, or depositing stains on the pool shell.

Iron bacteria in source water: Although not detectable with consumer pool-testing products, iron bacteria can be present in water and cause a pool-sized headache. These tiny organisms combine dissolved iron or manganese with oxygen and use it to form brownish deposits. In the process, the bacteria produce a brown slime that builds up on pool or plumbing surfaces.

These are some of the most important water types and waterborne pool invaders. And while each pool’s source water must be investigated individually, some generalizations can be made.

Look To The Source

In order to determine what’s in a customer’s water, journey back up the water main to find its history and origins. Different regions, different seasons, and of course, different delivery mechanisms influence its biological and chemical makeup.

Geography comes into play when determining whether water is likely too hard or soft. According to the U.S. Geological Survey, 89 percent of U.S. residential homes have water that is to some degree mineral-heavy or “hard” — some only slightly hard, and others like liquid, running rock.

Although broad generalizations are difficult, and exceptions are common, the American Southwest is distinguished by particularly hard water. Places such as Texas, New Mexico, Kansas, Arizona and southern California see some of the country’s hardest waters, with some measured mineral concentrations greater than 1,000 mg/L.

Moderately hard waters are likely to be found in the rivers of the Great Lakes states and the Pacific Northwest, while softer water is likely to be found in parts of New England.

Particularly now, in the springtime, heavy rains and snowmelt can reduce hardness in a pool, as both these sources are low in minerals. For those living near industrialized areas, these same spring rains are likely to be acidic, and this can wreak havoc on the water balance of pools. A higher buffer of total alkalinity (TA) is necessary to keep pH in a proper range due to that influx of low-pH water. (Pool professionals addressing the question should also be aware of the contribution that a high level of cyanuric acid has upon the total alkalinity reading. See the sidebar on calculating TA.)

Irrespective of physical location or season, individual municipalities may have an effect on source water, especially through the use of orthophosphate. Orthophosphate is a commonly used corrosion inhibitor that coats pipes and prevents lead from leaching into drinking water from aging water mains. Some of the cities that use orthophosphate include Washington D.C., New York City, Denver, and Detroit, among many others.

Where orthophosphate is used, high amounts of phosphate will be present in the fill water, providing a bounty for hungry algae to feed upon. A good dose of phosphate remover should be added to the water in this case; typical chemical formulations used in the pool industry for phosphate removal are lanthanum carbonate and lanthanum chloride.

Cheap Insurance

A few precautionary measures taken during a pool fill should provide insurance against the sort of pool problems discussed above.

First, know your source. Find out whether it has a history of producing problems. You can contact your local municipality to get information on water treatment systems. In addition, there are numerous resources online. One example is the USGS Web site, which provides well-organized information on water quality for individual cities and states.

Primarily, however, careful attention and experience in a particular area should inform a pool care professional’s assessment of local water. What has been seen in the past? Of course, the best places to seek this kind of information are seasoned pool care pros with years of experience with a particular water source.

Second, tie up what metals may be in the water with a metal sequestering agent. This provides insurance against any staining or metal precipitate problems that may be triggered either by the source water or by the addition of chemicals, which alter the pool’s chemical balance in their own right and can cause staining. In plain language, do not dump in a large amount of chlorine before metals have been sequestered, as this is one of the most common causes of early-pool-season staining.

Third, use chlorine-free shock to break down excess organics and disassociate metal bound to bacteria so that it can be sequestered.

Fourth, make sure you balance the water immediately. Balanced water ensures greater protection against damage to equipment or surfaces, and the sooner this is done the better. In addition, sanitizers work better at killing bacteria when water is properly balanced.

Fifth, use a clarifier and give the pool a good filtering; make sure to start with a clean, properly functioning filter. After filling and shocking there will most likely be lots of small-diameter waste material in the water. This needs to be filtered out and removed quickly to clear the water and enable the sanitizer to function properly.

Finally, begin normal sanitizing process. Having followed a few easy guidelines to ensure a good, clear start to the pool season, a summer of manageable pool water is likely to follow.

[Information for this article was supplied by Terry Arko, technical products specialist, SeaKlear, Bothell, Wash.]

Calculating TA (with CYA)

When testing uncovers a cyanuric acid (CYA) level over 50 ppm, pool professionals should calculate a third of that reading and subtract it from the total alkalinity (TA) reading.

  • Example: TA = 90 ppm, CYA = 60 ppm
  • Divide the CYA reading by 3 to get 20 ppm.
  • Subtract 20 ppm from 90 ppm = 70 ppm.

Even in very hard water, 70 ppm is too low. It is important for pool professionals to be aware of and adjust for this, as when alkalinity is too low, corrosive damage to the equipment can occur.


About Red Square Pools

Thank you for checking out our blog...we appreciate you taking the time to read our posts. To be quite honest, our posts come from your questions. Red Square Pool's wants to clear up the confusion and frustration of maintaining your pool and spa. We simply want to make Pool Maintenance and Repair SIMPLIFIED!! Let us know what your thinking by dropping us an email at Have a safe and happy swimming experience!

7 responses »

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