The Importance of Water Balance In Pools – Part 1

A woman diving into a swimming pool, with the words, RWF Management, The importance of Water Balance in Pools, Part 1

If maritime public health had its own version of the Oscars, the Academy Award for Best Chemical would probably be won by chlorine each year. Due to its low cost and natural disinfectant properties, chlorine is widely used in a variety of applications on ships to prevent and control the spread of harmful microorganisms, such as bacteria and viruses.

In recreational water facilities (RWFs)—aquatic venues like swimming pools and whirlpool spas for public leisure or therapeutic purposes—chlorine plays a pivotal role in keeping amenities safe and hygienic for bathers. Although chlorinating water is a reasonably straightforward process, the effective management of recreational water facilities is far from simple.

Just as a multitude of factors affect human health, the well-being of a recreational water facility is similarly multifaceted. In this three-part article we explore why there is more to “pool life” than just chlorine. Moreover, that maintaining the right chemical levels within the water, and ensuring there is a perfect balance between them, is crucial for both bather safety and the longevity of an aquatic venue’s infrastructure.

What Is Water Balance?

Maintaining balance and harmony is essential for a healthy lifestyle; the same principle applies to the water in aquatic venues. Properly balanced water creates an environment that optimizes the sanitation process, protects equipment and surfaces against corrosion and mineral buildup, and minimizes the likelihood of issues such as algae growth or cloudy water.

In simple terms, water balance refers to how various chemicals and minerals interact within the water. It is a concept that explains the tendency of water to dissolve (corrode) or deposit minerals (form scale) on the surfaces it comes into contact with.

The composition of pool water is in a constant state of flux, affected by various external factors ranging from the weather to substances introduced by bathers, such as perspiration, body lotions, and other personal care products. While a recreational water facility’s filtration and disinfection systems are designed to remove these pollutants, they cannot balance the water.

Without regular monitoring and adjustment by crew, water will naturally attempt to balance itself. When water lacks sufficient dissolved materials, particularly calcium, it becomes corrosive or “aggressive”. The water seeks to absorb its necessary minerals from the lining of a pool or from mechanical components such as pumps, heaters, and piping.

Alternatively, water with an excess of dissolved materials will try to find its equilibrium by releasing calcium carbonate, forming scale deposits on surfaces and machinery. This reduces the performance of pool filtration and circulation systems and increases maintenance requirements. The accumulation of scale also causes additional issues, such as diminishing the efficacy of chlorine or turbid (cloudy) water conditions.

There are five basic factors that influence water balance:

  • pH
  • Total Alkalinity
  • Calcium Hardness
  • Total Dissolved Solids (TDS)
  • Water Temperature

Prior to delving into these components, let’s turn the attention back to chlorine—the star of sanitation—to understand its composition and the impact is has when introduced to water.

A Short Explanation of Chlorine

Chlorine, derived from the Greek word “chloros” meaning “greenish yellow”, was first discovered in 1774 by Swedish-German pharmaceutical chemist, Carl Wilhelm Scheele. Represented by the symbol Cl, chlorine is a member of the periodic table’s 17th group, alongside fluorine (F), bromine (Br), iodine (I) and astatine (At).

Originating from two Greek words—”hal” meaning “salts” and “gen” meaning “to produce”—this group of chemical elements is known as “halogens” as they produce salts when reacting with metals. For instance, the reaction between chlorine and sodium (Na) results in the formation of sodium chloride (NaCl), commonly referred to as ”salt.”

Chlorine, which is gaseous in its elemental form, is frequently employed in various compounds to effectively sanitize pool water. These include the liquid form of sodium hypochlorite (NaClO), typically referred to as bleach, and calcium hypochlorite tablets (Ca(ClO)₂).

In addition to being a powerful disinfectant, chlorine also serves as an effective oxidizing agent, facilitating the breakdown of organic substances like sweat and body oils. This dual functionality underlines chlorine’s indispensable role in preserving water cleanliness and clarity within aquatic venues.

What Happens When Chlorine is Added to Water?

When introduced into a recreational water facility, an initial chlorine dosage first reacts with any inorganic and organic materials within the water. These reactions consume chlorine, with the amount lost during the process known as the Chlorine Demand.

After chlorine demand has been satisfied, the remaining chlorine in the water is known as the Chlorine Residual. Chlorine is a residual sanitizer, meaning its efficacy persists long after its initial application, providing ongoing protection against contaminants. Residual chlorine levels are commonly expressed in units of parts per million (ppm) or milligrams per liter (mg/L).

The chlorine residual is further divided into three categories:

  • Free Chlorine: The chlorine remaining in its original form serving as an indicator of the concentration available for disinfection purposes. Free chlorine is highly effective in eradicating pathogenic microorganisms.
  • Combined Chlorine: Created when free chlorine binds with contaminates such as ammonia and nitrogen compounds, combined chlorine—collectively referred to as chloramines—is the source of the noticeable “chlorine smell” often associated with public recreational water facilities. The presence of combined chlorine indicates that contaminants are present in the water and that they are actively being neutralized.
  • Total Chlorine: Represents the overall amount of chlorine in the water. Total chlorine is equal to the sum of free chlorine and combined chlorine concentrations.

When chlorine is added to water, hypochlorous acid (HOCl) and hypochlorite ions (OCl-) are formed: free chlorine is the combination of these two components. Hypochlorous acid is the active sanitizing form of chlorine, while hypochlorite ion is the “reserve team,” waiting to covert to hypochlorous acid as the HOCl is used up. Hypochlorous acid is a highly effective disinfection agent; hypochlorite ions, less so.

Free chlorine denotes the concentration of hypochlorous acid and hypochlorite ions present in the water that have not yet reacted with contaminants.

This is why the free chlorine residual is the most important type to monitor from a public health perspective because it represents the amount of chlorine available to eliminate pathogens. It acts as a safeguard against additional microbial contamination that, in the case of aquatic venues, can be introduced as more bathers enter the facility.

The hypochlorous acid and hypochlorite ions remain in equilibrium with each other: the pH of the water determines the ratio of the equilibrium.

What is pH?

In the maritime public health Oscars, pH would most certainly be nominated in the Best Supporting Actor in a Water Production category.

pH refers to the “potential of hydrogen” or “power of hydrogen” and is measured on a logarithmic scale from 0 to 14. The scale is used to denote the acidity or basicity of an aqueous solution: a solution in which water is the solvent (i.e., the component present in the greatest amount).

pH is determined by the concentration of hydrogen ions present. Hydrogen ions (H+) are essentially protons that are formed when acids dissolve in water and a hydrogen atom loses its electron. Therefore, in essence, pH measures the activity of hydrogen ions in water, which is a key factor in its chemical behavior.

In pure water—distilled water that has been filtered or processed to remove impurities—the concentration of hydrogen ions equates to a pH value of 7. Lower pH values have a greater concentration of hydrogen ions which corresponds to a higher acidity. Conversely, a diminished presence of hydrogen ions results in a pH value above 7: the higher the pH, the stronger the basicity, or alkalinity, of the water.

How pH Affects Water Balance

In water balancing, pH is of fundamental importance as it influences the equilibrium of all other chemical parameters and the overall quality of the water. Rapid swings in pH—also known as “pH bounce”—have a substantial impact on water balance. Different elements can cause the pH to fluctuate including dirt, rain, bather pollutants, or any other external substances entering the water. Adding chlorine also affects pH.

pH levels in recreational water facilities should be maintained between 7.0 and 7.8. To ensure the most comfortable environment for bathers while balancing the effectiveness of chlorine’s sanitizing power, the optimum pH range is between 7.4 and 7.6.

In the chemistry of free chlorine, hypochlorous acid is a more potent sanitizer compared to hypochlorite ions. This is attributed to its superior oxidizing properties and enhanced capacity to infiltrate and dismantle the cellular barriers of pathogenic microorganisms. Its effectiveness as a sanitizer is dependent, however, on pH.

As pH levels in the water decrease, the reaction shifts to produce more hypochlorous acid, leading to an accelerated consumption. This means that while chlorine is more effective at a lower pH, its reserves are depleted faster, necessitating a greater frequency of replenishment to maintain its sanitizing power. In other words, the facility will use an increased amount of chlorine to achieve the desired results.

Consequences associated with a pH level that is too low include the erosion of a facility’s metal fixtures and components, as well as surface etching. Furthermore, a bather’s natural oils will be stripped away leaving dry, itchy skin. Bathers may also experience severe eye inflammations, such as redness, puffiness, or burning.

As pH rises, hydrogen ions begin to disassociate with the hypochlorous acid diminishing the overall efficiency of the chlorine. At a pH of 8.0, the equilibrium shifts such that approximately 25% of the available free chlorine is in the form of hypochlorous acid, meaning only a quarter of the free chlorine in the water is actually working to control disease-causing pathogens.

High pH levels can also result in:

  • Cloudy water
  • Potential calcium scaling issues which damage the aesthetic of aquatic venues and put a strain on filtration systems leading to circulation issues and even potential equipment failure
  • Bather irritation such as skin rashes and nose and eye inflammations

Maintaining the correct pH level is therefore crucial in ensuring hypochlorous acid is the dominant form in the free chlorine residual. If the pH level is too high, introducing muriatic acid or sodium bisulfate into the water will lower it. If the pH level is too low, adding sodium carbonate will raise it.

Dosages for these chemicals will vary depending on the particular product used, the initial and target pH levels, and something known as the total alkalinity, an element we will discuss in the second part of this article. We’ll also tackle three remaining components—calcium hardness, total dissolved solids, and temperature—that influence water balance in an aquatic venue to complete this series regarding the importance of water balance in RWFs.