Limescale caused by hard water can wreak havoc on any type of appliance, system, pipe or valve that water runs through. Due to drought in various parts of the U.S., hard water is becoming more of a nuisance because of constant changes in the water table and groundwater quality. The challenges facing any business involved with maintaining water distribution systems today are extreme. Yearly maintenance and repair costs to water systems add up to many millions of dollars in certain areas of the U.S., and groundwater is only getting harder.
According to the U.S. Geological Survey, patterns of hardness vary across the U.S. Water hardness is based on major ion chemistry concentrations, which are relatively stable in groundwater and generally do not change over time.
The softest water is found in parts of New England, the South Atlantic/Gulf states, the Pacific Northwest and Hawaii. Moderately hard water is common in rivers in Alaska and Tennessee, the Great Lakes region and the Pacific Northwest. Hard and very hard water is found in some streams in most of the country. The hardest water was measured in streams in Texas, New Mexico, Kansas, Arizona and California.
Damage & Disease
Wikipedia defines limescale as “the hard, off-white, chalky deposit found in kettles, hot water boilers and the inside of inadequately maintained hot water central heating systems.” The article noted that limescale often is found on the inner surface of old pipe and other surfaces that have been subjected to hard water. Limescale is damaging to plumbing components and appliances, and can be difficult to remove.
Wikipedia defines hard water as “water that has high mineral content ... [It] is formed when water percolates through deposits of calcium- and magnesium-containing minerals such as limestone, chalk and dolomite.” The article pointed out that, although hard water is not a health hazard, it can damage boilers, cooling towers, water heaters and other water-handling equipment.
High levels of hard water ions such as Ca2+ and Mg2+ can cause scaly deposits in plumbing, appliances and boilers. These two ions also combine chemically with soap molecules, resulting in decreased cleansing action. According to the American Water Works Assn., ideal-quality water should not contain more than 80 mg/L of total hardness as CaCO3. High levels of total hardness alone, however, are not considered a health concern.
A report by the Salt Institute in October 2013 linked research of Legionnaires’ disease to lime-scale deposits. The vast majority of cases of legionellosis are the result of exposure to Legionella through a water system. Any place moisture can build up, such as hot tubs, air conditioning systems, hot water tanks or plumbing systems, can cause bacteria such as Legionella to grow. Limescale deposits in the water system allow bacteria to grow and potentially infect those using or exposed to the systems.
ASHRAE identifies the conditions in a building’s water system that make it less likely for Legionella to grow and spread, and recommends maintenance procedures and hazard controls to stop the spread of the bacteria. The standards are aimed at building/facility owners and managers, but they also are useful to professionals involved in designing water systems, to ensure their practices are adequate to prevent Legionella exposure.
The degree of hardness standard as established by the American Society of Agricultural Engineers (S-339) and the Water Quality Assn. (WQA) is displayed in Table 1.
According to WQA, the three basic categories for remediating hard water and limescale are:
- Chemical softening: lime softening, hot and cold; lime-soda softening;
- Membrane separation softening:
- nanofiltration; and
- Cation exchange softening: inorganic, carbonaceous or organic base exchangers.
Traditional Softening Systems
For traditional limescale prevention, the technology of choice always has been ion exchange water softening systems, especially when it comes to commercial water distribution systems. Softeners have come under scrutiny in the past 10 years due to the salt they discharge into the environment and the amount of water they waste; however, they still provide the best overall protection against corrosion from limescale.
A large-scale study conducted by the Battelle Memorial Institute and commissioned by the Water Quality Research Foundation in 2009 found that “adding a water softener helps water heaters and major appliances operate as efficiently as possible, while preventing clogs in showerheads, faucets and drains.” The study also found that water heaters could maintain their original factory efficiency ratings for as long as 15 years when using softened water. With hard water, efficiency was reduced by up to 48%. Hard water affected both electric water heaters, in which the heating elements could be damaged by scale, and tankless water heaters, some of which failed after only 1.6 years.
Additionally, the Battelle study found that showerheads performed better with softened water—with hard water, some showerheads’ capacities were reduced by 75% in less than 18 months. Faucets also were negatively affected by hard water, with strainers clogging in days in some cases. A study conducted in 2013 concluded that water softeners virtually eliminate energy-wasting, service life-shortening scale accumulation on gas and electric water heaters. Another recent study concluded that softeners set with appropriate salt efficiency do not harm septic systems, and may actually improve their effectiveness.
Despite these studies, many cities in California have banned ion exchange softeners. This is primarily due to the salt deposited into the drain from the backwashing procedure. As a result, many water treatment dealers provide an exchange tank service and charge a monthly rental fee, eliminating any salt or backwashing issues. According to John Foley of Rayne Water Systems, commercial water softeners remain a top treatment option when a point-of-entry solution is needed. When valves, resin, configuration and proper installation are in alignment, softener systems provide 30% to 40% higher efficiency. These factors play a critical role in the efficiency and efficacy of ion exchange systems, but many systems today are not properly maintained. As a result, they can pose an environmental impact.
Chemical Treatment Solutions
Chemical softening has long been a treatment of choice for hard water due to its cost-effectiveness. One of the oldest treatment options—phosphates—has been shown to offer continued protection from limescale buildup in water distribution systems.
According to the Phosphate Facts website, “Experience has shown that polyphosphates not only inhibit scale formation, but they can also help remove existing hard deposited carbonate or sulfate scale.” It describes how potable water pipe that has been treated with polyphosphate over several months shows improvement slowly, as scale begins to disintegrate. As the scale softens, the particles are deflocculated and can be carried away through the pipe system.
The website also noted that “polyphosphates, alone or in combination with orthophosphates, can effectively control corrosion on both ferrous and non-ferrous metals and alloys. Polyphosphates are particularly effective as corrosion control agents at lower temperatures and at a pH of less than 7.5. They have also been shown to be effective in brackish water (greater or equal to 2,000 ppm sodium chloride, or NaCl) with corrosion reductions of up to 90% being reported.”
For commercial water treatment, a commercial polyphosphate system distributed by ScaleZERO Systems employs a stainless steel vessel and several polyester pleated sediment filters from United Filters Intl. Each filter contains several spheres composed of an NSF/ANSI Standard 61-approved hexapolyphosphate media called Siliphos, which is especially effective in water heater systems due to its efficacy in hotter water. This system is modular and can be configured for flow rates of more than 100 gal per minute with inlet sizes up to 6 in., making it an ideal alternative to traditional salt-based water softeners for both tankless water heaters and boiler systems.
Simpler systems are offered by tankless water heater companies such as Takagi, which began marketing a residential treatment system in 2002, when tankless water heaters were first introduced. The company always has maintained that education is key to any prevention technology. Now owned by AO Smith, it employs a system using template-assisted crystallization (TAC), a catalytic media process that transforms minerals into harmless, inactive microscopic crystal particles that pass to the drain. It is a scale prevention device with proven third-party laboratory test data and years of successful commercial, residential and food service applications. AO Smith uses studio online streaming and hands-on local training to educate its customers on the need for protecting water heaters and boilers.
Media marketed under the brand names Next and Filtersorb SP also have had successful track records as water softening alternatives, and claim a spot in the realm of environmentally friendly products using TAC technology.
Other Scale Control Technologies
Other technologies tout scale control, such as magnetic, electromagnetic and electrostatic
devices, but their efficacy remains unknown. Magnetic treatment consists of passing hard water through a magnetic field. Promoters of magnetic devices claim that this simple operation provides a scale control method, even for water with a high tendency for scaling. It also is often claimed that magnetic exposure can inhibit corrosion.
Priority for Prevention
There are a multitude of technologies that can help protect water distribution systems and equipment from limescale. The fact remains that many commercial and facilities maintenance businesses today do not provide protection for their equipment, resulting in many millions of dollars spent in unnecessary repair costs. This, too, can provide opportunities for water treatment distributors and dealers to evaluate and educate their customers.
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