Test the Tap Water. Water Chemistry Starts at the Tap.

If you do not know the chemistry of the source water, making decisions about how to treat your pool become more difficult. This article covers the importance of knowing the chemistry from the tap.

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Test every pool's tap water 

Let's start by defining the term "tap water", because some people may call it tap water, "source water", "fill water", "hose water", etc.  Tap water simply refers to the water that fills a pool, whatever that source may be. Usually, it's a hose from the house, or from a well. Assume everyone's tap water chemistry is different, even if they are in the same neighborhood. Without knowing the water chemistry from the source, we pool professionals have no baseline of understanding. This is especially important for new plaster startups and re-openings for the summer season.

It's incredibly important to write down tap water chemistry and be honest about it. Be diligent in how you test...shortcuts in testing can lead to chemistry problems down the road.

Customers depend on pool professionals to do the right things and treat their pools properly. The responsible thing to do is to test and record the tap water chemistry. Think about it...water evaporates and is splashed out, so the pool constantly needs to be topped off. If we don't know what the tap water chemistry is, we put ourselves at a severe disadvantage.

What to test for, and why

  • pH. Whether we like it or not, pH likes to fluctuate in a pool. Normally, water out of the tap is slightly alkaline, which has a direct impact on chlorine efficiency. If our fill water is acidic for some reason, that will have an effect on the pool's pH too. pH also affects the type of alkalinity present and the LSI. Pool additives later can correct pH, but only if we know what to correct.
  • Alkalinity. Test for total alkalinity, as it is a measure of all dissolved alkali in your water (ppm). Read more about the relationship of pH and total alkalinity here. Learn more about alkalinity here, and since the LSI calls for carbonate alkalinity, we have an article for that too.
  • Calcium hardness. This one is major. We were at a pool recently that had a calcium hardness reading of about 250 ppm. Yet the pool surface was clearly etched and pitted. It looked green and awful. So we tested the fill water...and just as we suspected, the calcium level from the tap water was just 40 ppm, which is low.  Is it any wonder how the hardness level in the pool climbed up from 40 to 250 ppm?  Nope. The plaster surface donated the calcium to the water, because water seeks equilibrium. We at Orenda stress the value of calcium because of its remarkable consistency, which provides us a solid foundation for a good LSI. Calcium management is so critical, it is the first of our Four Pillars of Proactive Pool Care.
  • Metals. Most pools get their water from municipal treatment plants, which send water through a series of pipes. It is not uncommon for some of this infrastructure to be metal, which can be dissolved into the water stream. In an extreme case, think of the water crisis in Flint, Michigan. Water is the universal solvent, which means it can pull metals into solution. For swimming pools, the metals most commonly found are copper, iron, and manganese. These metals can get oxidized and stain your pool. We recommend using a metal filter to capture those metals before they get in your pool. Even pools that are filled with water from a delivery truck can have issues.
  • Phosphates. Testing for phosphates is directly related to the previous two items: calcium and metals. Why? Because in the past decade or so, municipalities around the country have been putting phosphonic acid into drinking water as a sequestering agent. They do this for many reasons, which you can research on your own...but the point is that phosphates are often introduced to pools via the fill water. Depending on where you live, well water may also be high in phosphates.
  • Free chlorine. Would you be surprised if we told you that tap water can have 1.5 ppm free chlorine in it? Well, it's true. We test water all over the place and have seen it. 1.5 ppm is a great number for commercial pools to operate on! Yet we drink it. Bottom line, test chlorine levels.
  • Combined chlorine. While many places add free chlorine for disinfection, others add chloramines to their water supply. Why? Because chloramines react slower in the disinfection process than free chlorine and can carry through the pipes longer to still be present in the water at the tap. Having chloramines present means more chlorine consumption at first, due to breakpoint chlorination. We encourage you to research this on your own, but it is not uncommon for pools to be pouring in fill water that has combined chlorine levels over 0.2 ppm. Can you say "air quality problems"?
  • Total dissolved solids (TDS). Especially in areas like Southern California that often restrict draining, knowing the TDS makes a big difference for old, rarely-drained pools. Not that TDS in itself is a problem for chemistry, it just continues to add up, and high levels of TDS start to really impact the LSI. The more TDS you have, the more aggressive the water (lower LSI).

Baseline testing can protect you

Anyone working with pools should test fill water (and record it) before doing anything else. This goes for construction companies, pool designers, and especially operators.

Why designers? Because knowing the base chemistry of the source water can help determine what type of equipment and chemicals to use. For example, if the source water has very low calcium hardness, cal-hypo may be a good chlorine choice for that pool. If the calcium hardness is really high, liquid chlorine (sodium hypochlorite) may be a better choice.

As for pool startups, construction companies and plaster applicators need to know what's in the water because it immediately affects the plaster in its most vulnerable time. The Orenda Startup™ is based on testing tap water and pre-treating water to an LSI target. But if we don't know what is filling the pool, we cannot to the startup properly. Every decision made in the startup procedure is rooted in the chemistry from the source water.



If you're not testing, you're just guessing. Know the water you're working with. No exceptions. 

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