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Chemical Solutions

When it comes to watershapes designed for human interaction – including pools, spas and fountains – the chemical treatment of the water is a key safety issue that can be handled in a variety of ways. Indeed, says water-chemistry expert Jeff Freeman, so many products and so many approaches are available that the average designer or builder could probably use a bit of guidance to help them keep everything straight, both for themselves and their clients.

Water is one of the planet’s most dynamic and complex chemical compounds. On its creative side, dyhydrogen monoxide (H2O) acts as the matrix for a variety of compounds that engender plant and animal life. On its destructive side, it is an agent that corrodes, dissolves and precipitates mineral compounds.

As watershapers, our challenge is to work with all aspects of water’s active character – a challenge that has occupied chemists, hydrologists and biologists for generations. Indeed, we are all caught up in the same longstanding, collective effort to transpose to artificial systems a set of processes that exist in nature to balance and sanitize water.

Meeting the demand for clean, clear water in recreational and decorative environments is no small task, especially when those systems are designed for bathing, swimming and possible ingestion. In fact, whether we look at it as a construction material or as an aesthetic medium, managing the water is every bit as critical to our success as are structural engineering, hydraulics or materials selection.

Fortunately, humans are inventive, and there’s a grand history of engineered solutions that counteract water’s inclination to harbor and encourage bacteria, viruses, algae, insects and chemical toxins. From the smallest wading pools to the most glorious commercial pools, we are able to participate in aquatic environments because of clear-headed and effective application of techniques and technologies that simplify what we do in keeping water clean and pristine.


It’s safe to assume that human beings, since the dawn of time, have sought to immerse their bodies in water for the full and obvious range of recreational, health and spiritual reasons. By the time we decided to contain water for drinking, swimming, bathing and luxuriating, it was certainly recognized that we either had to replace the water continuously or treat it in some chemical way.

The baths of the Roman Empire dot the map from Asia Minor to the Iberian Peninsula and from North Africa to England. Their designers installed copper and silver plates in the feed-water systems that were eroded as water flowed into the baths. Thousands of years ago, in other words, watershapers recognized that the dissolution of silver and copper in water reduced algae growth and made the water safer.

Sanitizer Sanity

Positioned at number 17 on the Periodic Table of Elements, chlorine is one of the “halogen” family of elements, a grouping that also includes, fluorine, bromine and iodine.

Among all the halogens, chlorine stands as the leading means of sanitizing drinking water and the water in swimming pools, spas and other interactive waterfeatures. To meet these needs, suppliers have developed a number of chlorine compounds – sodium hypochlorite (liquid bleach), calcium hypochlorite (granular), trichlor and sodium dichlor (tablets and powders) and lithium hypochlorite (granular) – to go along with elemental chlorine (gas).

One of the other halogens is bromine, which, like chlorine, can be used to kill bacteria in water. Bromine (number 35 on the Periodic Table) is different from chlorine in that when it is used to sanitize water, it does not produce the bothersome “chlorine smell,” which makes it a wonderful choice for indoor pools and spas where the fact that it is readily destroyed when exposed to sunlight becomes irrelevant.

It’s a case where a bit of knowledge on the part of the system designer or builder is helpful indeed: Where stabilized chlorines are not the best choice for indoor pools because of odors – and where their use indoors is not essential because the water is effectively shielded from the sun – bromines have complementary properties that make them well suited to indoor use.

— J.F.

Only recently have biologists confirmed what the Roman watershapers already seem to have known on some level: that silver ions work to kill and retard the development of many types of bacteria and that copper ions slow the growth of and kill algae.

For the most part, however, the pools, baths and fountains built before the Industrial Revolution in the 19th Century relied on draining and replacement of water – your basic fill-and-draw systems. With the advent of chlorine as a water sanitizer at the end of that century, however, the picture changed forever: When chlorine was added to public water systems, rates of infection by waterborne diseases dropped to the point where many diseases, including typhus, typhoid and dysentery, all but vanished in the industrialized world.

Nobody knows where or when the first swimming pool was treated by chlorine, but it’s easy to presume that some form of sodium hypochlorite (liquid bleach) was added manually from a bottle. The enduring effects of that simple turn of the wrist have been profound: Today, the vast majority of the world’s millions of pools, spas and fountains are treated with chlorine-containing compounds.

Chlorine chemistry and the industry that grew up around it flourished in the 20th Century, marked by the development of various dosage forms. We still have liquid chlorine, but it’s been joined by tablet, granular and gaseous versions that are all easily soluble in water.

Along with them came a range of devices we use to add chemicals without the need for physical contact with chlorine on the part of homeowners or service providers. These technologies have been developed in the names of both convenience and safety – and they’ve since been joined by dozens of variant technologies that all aim to do the same job of making the water safe for use.


Whenever a person dips into the water, they add organic compounds to it in the forms of sweat, urine, skin, blood, saliva, dirt, cosmetics and suntan lotion. This is a challenge to water sanitization, because all of those additions bring organic chemical compounds to the water that consume chlorine and other sanitizers and give rise to bacteria and algae.

These compounds are consumed by chlorine in the process known as oxidation. Basically, chlorine “burns up” the organics it encounters in the water in the same way it does bacteria and algae. What this means is that, in the course of normal usage, watershapes consume chemicals in commensurate levels to meet bather demand. Likewise, as dirt, debris and fertilizers find there way into the pool, they too consumer sanitizers and oxidizers.

Somewhere along the line, it was recognized that adding these chemicals by hand (using the bottle-at-the-end-of-the-arm method) was grossly inconvenient, especially for large bodies of water that served the needs of large numbers of people. Before long, we were looking for ways to do the dosing automatically.

The developmental history of these chemical-feeding methods is well beyond the scope of this article; what we will cover instead is the need among designers and builders to know how to sort out the numerous and sometimes confusing options available to us in the here and now as 21st-century watershapers.

One thought that must be overcome in sorting things out is the notion that people who service and maintain watershapes are the sole custodians of the water. To be sure, they play major roles, but the professionals who design, engineer and build the watershapes have an equal if not greater role in setting the stage for everything that follows.

In fact, I’d argue that the opportunity to specify or place chemical feeders and generators during system development puts complete responsibility at the feet of the watershapers and requires them to make wise, informed choices well before any technician arrives on site.

With that as our context, let’s review the available technologies (starting with the simplest) and consider their advantages and drawbacks.

[ ] Floating Feeders: To this day, the most familiar of all chemical feeders is the floating feeder. Historically, however, this is actually among the more recent developments and arose from the need to sanitize pools with virtually no effort and at minimum cost. “Floaters,” as they’re widely known, were made possible by the development of chlorine tablets, specifically in the stabilized, ph-neutral form known as “trichlor.”

These slow-dissolving tablets of chlorine float in feeders across pools ranging from the most inexpensive abovegrounds to the most exotic concrete pools and add chorine without any human effort at all beyond the occasional need to add fresh tablets.

Floaters, however, are grossly imprecise: They are not, for example, able to treat pools according to real “chemical demand” or in large quantities. When they get stuck in one part of the pool (which often happens), they also create highly treated pockets of water that disperse only slowly. Finally, critics of floaters point out that children sometimes play with floaters, which are sometimes decked out as animals and look a bit too much like toys. As a result, kids can be exposed to heavily treated concentrations of water that may be harmful to them.

[ ] Erosion Feeders: Tablet-form chlorine’s ability to provide sustainable sanitizer residuals in water was further advanced by simple erosion feeders. These ingenious devices consist of containers that store chlorine products and are plumbed in line with a watershape’s return system. Water flowing through the feeder gradually erodes the tablets, releasing dissolved chlorine compounds directly into the body of water.

The primary advantage of trichlor tablets is that they are formulated with isocyanuric acid, a stabilizing compound familiar to pool-industry people but perhaps less well-known among landscape architects and fountain builders. Its inclusion is significant because the active form of chlorine – hypochlorous acid – is extremely susceptible to ultraviolet degradation in sunlight. When cyanuric acid is dissolved in water, it protects the chlorine content from UV degradation.

Thus, erosion feeders offer the dual advantage of treating water with “stabilized chlorine” for controlled, longer-term protection.

The problem with erosion feeders is that they are still, for all their virtues, quite imprecise. The amount of chemical added to the water is dependent upon the size of the feeder relative to the flow of water through it. In addition, the tablets are incapable of responding to peak demands because they are designed to dissolve slowly. So in spas or high-use watershapes of any kind, there will be times when proper sanitization requires intervention of the bottle-at-the-end-of-the-arm variety.

[ ] Metered Solutions: The other basic approach to chemical feeding involves the use of chemical pumps that draw metered amounts of liquid chemicals from a reservoir at preset intervals and in preset quantities. These systems rely on liquid forms of sanitizing chemicals, generally sodium hypochlorite. These metered-chlorine systems generally consist of drums of bleach with tubing and small feeder pumps that draw fluid from the drum as the timer dictates.

Two pump technologies have dominated this market for decades, one being the peristaltic pump, the other being the diaphragm pump. Both are compact and in their modern incarnations provide adjustable timing that enables variable amounts of chemical injection in response to need.

[ ] Oxidation Reduction Potential (ORP): The activity of a sanitizer can be monitored by measuring a small electrical current passing through the water from one electrode to another. ORP meters can sense drops in the “oxidation reduction potential,” indicating a decrease in sanitizing action and triggering a chemical pump that raises the sanitizer level.

These systems have proved remarkably effective in pools subject to heavy bather loads and/or varying bather loads and have the great virtue of releasing sanitizers into the water as needed. This helps in avoiding dramatic peaks and valleys in sanitizer residuals, which in turn aids in maintaining balanced water and ensuring that bathers will be not be exposed to water with either too little or too much sanitizer.

ORP meters are often paired with automatic pH controllers. These systems electronically monitor pH levels and will add acid or base chemicals to the water whenever the pH level moves beyond preset ranges – typically pH 7.6 to 7.8.

[ ] Ozone generation: The use of ozone (O3) as a sanitizing option has gained popularity in the past few decades, particularly in treatment of high-use pools. It is essentially an unstable form of oxygen that is generated by two basic technologies, one using corona discharge, the other using ultraviolet light.

Corona-discharge units generate an electrical field that is similar to the activity in lightning: When dried atmospheric oxygen is drawn through the corona-discharge chamber, its molecules are broken down to create ozone that is then injected into the watershape’s circulation system. In an ultraviolet system, air is exposed to intense UV light, which also has the ability to produce the unstable O3 molecule.

Pound for pound, ozone is 1,000 times more potent a sanitizer and oxidizer than is chlorine, but it’s also less stable and lasts no more than 18 minutes when dissolved in water. This means that ozone systems are most effective when run constantly. Corona-discharge systems produce many times the ozone UV systems do, are much more expensive and are well suited to large-scale applications on public pools, for example. For their part, UV systems are most commonly used on small systems such as spas.

Because ozone is so unstable, watershapes treated with it must also be treated with another sanitizer, usually chlorine or bromine. Bromine is often preferred in conjunction with ozone systems because active bromine is regenerated by ozone. In this sense, bromine works synergistically with ozone, while chlorine works separately from it.

[ ] Copper/silver ions: As mentioned above, the Romans knew that metal ions helped maintain safe water. It has since been scientifically proved that copper ions will kill and retard the growth of algae, while silver ions will act as a mild bactericide.

Today, various copper/silver-ion systems are used, primarily on swimming pools, to help reduce the “work” performed by mainline sanitizers such as chlorine or bromine. As is the case with ozone systems, these devices cannot be used without the support of a separate sanitizer and oxidizer.

[ ] Saltwater chlorine generation: Based on the dynamics of seawater, one of the most proficient technologies developed to date for water sanitization is the saltwater chlorine generator. We all know that ocean water contains salt. What most of us aren’t aware of is that the photosynthetic activity of plant life in the ocean generates small electrical charges that interact with the salt in the ocean water to generate trace levels of chlorine, iodine and phosphorus. Although the concentrations are almost immeasurably small, these chemicals provide some sanitizing action.

Saltwater chlorine generation works in much the same way: Salt is added to a pool at a concentration of about 3,500 parts per million – about a tenth of the salinity of the ocean. The water then circulates through a chamber that houses a set of electrodes. As current passes through the water, the sodium chloride is converted to sodium hypochlorite (liquid chlorine). The owner or operator just adds salt from time to time, and the chlorine residual is maintained at a relatively constant level.

One of the advantages of this technology is that it provides for constant super-chlorination. As water passes by the electrodes, the concentration of chlorine in the small chamber is extremely high – more than sufficient to “shock” the water and oxidize the unwanted chloramines compounds responsible for the familiar “chlorine smell,” burning eyes and other bather discomforts.

Saltwater chlorine generators can be combined with ORP meters, thus providing for a remarkable level of control over sanitizer levels.

[ ] Bromine generators: The active form of bromine – that is, hypobromous acid – can be generated in very much the same way as saltwater systems generate chlorine. The one key difference is that in a bromine generation system, the “salt” is sodium bromide rather than sodium chloride.

Largely because of bromine’s susceptibility to UV degradation when exposed to sunlight, bromine generators have primarily been used with portable spas, which remain covered most of the time, or for applications with indoor pools and other interior watershapes.


The application of any of the technologies listed above is influenced by standards issued by state and local health departments, the Centers for Disease Control and industry associations including the Association of Pool & Spa Professionals (formerly NSPI) and other organizations.

Downstream Addition

It’s a rule with very few exceptions: Whenever you’re adding chemicals to contained, controlled water using some type of feeder or sanitizer-generation technology, they must be added after the water has been filtered and heated.

The reasons for this are straightforward: First, it makes little sense treat the water before it’s been filtered, because the filter removes dirt from the water and reduces the work to be done by the sanitizer and oxidizer. It doesn’t take a chemist to figure out that treating clean water requires less chemical input than does treating dirty water.

Second, sanitizing chemicals such as chlorine or ozone are highly corrosive. When they’re added upstream of the equipment, they are more likely to damage metal components, particularly the copper heat exchangers in most types of heaters. This is one reason why placing chlorine tablets in skimmers – a common practice in the absence of a more advanced feeding system of the sort discussed in the accompanying article – is not a good idea.

— J.F.

These standards declare that chlorine residuals for residential pools and spas, for example, generally should be maintained between 1 and 3 parts per million. The recommended levels for commercial pools vary a bit more from place to place depending upon the experience and requirements of a given health department, but the common recommended range is a residual from 3 to 5 parts per million. The same organizations also stipulate levels for bromine residuals and other factors including water hardness, pH, total dissolved solids and stabilizer levels.

In all cases, the challenge to the watershape designer is finding a system that will maintain the water within specified limits consistently and over time. Most of the water-treatment systems discussed here came into existence to meet these needs both reliably and efficiently.

It’s beyond the scope of this article to delve into the water-chemistry issues that can be involved in the system-selection process; rather, the intention is to help watershapers develop a working familiarity with treatment options and position yourself to make informed and appropriate recommendations to your clients.

A watershape equipped with a suitable chemical-feeding system stands a better-than-average chance of remaining pristine for the long haul. Watershapes for which these choices are left for “later,” however, may not be quite so fortunate.

Jeff Freeman is director of technical services and commercial sales for Balboa Instruments of Tustin, Calif., and is also founder of Fluid Logic, an independent hydraulics-consulting firm in Upland, Calif., that specializes in complex aquatic systems. He entered the watershaping industry more than 20 years ago,working for a wholesale distribution firm. He later established his own service and repair company, then returned to the distribution business as a product representative working with swimming pool and spa builders. He has extensive experience designing and troubleshooting hydraulic systems and has taught the subject at the California Polytechnical University in Pomona, Calif.

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