Microorganisms: The effects of on-site water treatment
by Abigail Cantor, P.E.

This article is part of a series discussing the growth of microorganisms in plumbing systems.  As previously noted, many types of on-site water treatment equipment create conditions for microorganisms to grow and thrive by increasing the residence time of the water in the plumbing system with extra water storage volume, providing additional surface area for microorganisms to form biofilms on, and removing or using up any available disinfection to fight microorganisms.

The best practice in plumbing design is to provide on-site water treatment only when it is absolutely necessary to do so.  It is also important to select the appropriate treatment system, to determine a proper location for the equipment in the plumbing system, and to size the equipment so that volume and surface area are minimized.  Finally, automatic clean-in-place systems or manual cleaning protocols must be utilized to keep the equipment free of biofilms.

Determining Necessary Water Treatment

The first step in plumbing design is to determine specifically what contaminants, if any, are of concern in a building’s water source.  To do this, one must consider that there are numerous chemical compounds and types of microorganisms that can potentially contaminate drinking water.  Contaminants are identified and regulated in the United States with separate standards for municipal water systems, private water systems, and bottled water.  See Table 1.

If the building is connected to a public water system, the water has already been rigorously tested for the list of contaminants listed in Tables 2 and 3.  The results of those tests are public record, available at the regulatory agency that governs the state or territory where the building is located.  The results are also sent to each water utility customer annually in the Consumer Confidence Report.  There might be local issues to be concerned about, such as increasing concentrations of an industrial chemical in a public well.  In that case, the property owner should keep track of water utility plans to resolve the problem and attend water commission meetings, read the water utility website, or call the water quality manager.  If a building owner is not comfortable with the utility’s approach to removing the contaminant threat, then an on-site water treatment device should be used for removal.  It would be a rare and special case to need such a device.

It is possible for building plumbing systems to receive debris from municipal water distribution system piping.   Debris occurs in the distribution system when particles, like sand, settle out and when dissolved chemicals in the water, like manganese, iron, or aluminum, chemically precipitate out.  The possibility varies with the nature of the water and the water utility’s pipe cleaning and replacement program.  Debris can temporarily be entrained in the water during utility or road construction; it can happen seasonally due to water main flushing and other routine maintenance activities.  If a property owner experiences discolored water at an intolerable frequency, then on-site removal of the debris may be desired.

There is also the possibility that a building’s plumbing system leaches contaminants into the water.  Lead, copper, and iron are known to transfer from piping materials into water to varying degrees depending on characteristics of the individual water system.

If the property owner owns the water source, such as a private well, they must take the responsibilities of a water utility manager.  After complying with any state regulations on water quality for private water sources, the property owner must decide what other contaminants they might want to test for and, if significant, remove.  See Tables 2 and 3.  A common issue for private wells is high iron concentrations which can precipitate out and stain sinks and laundry.

For both private water sources and municipal water, the hardness of the water can be an issue.  Water hardness is mostly a measure of calcium and magnesium concentrations in the water.  Depending on other characteristics of the water, including temperature, the calcium and magnesium can precipitate out of the water as solid compounds.  The solids can cover heating surfaces in hot water heating systems, which in turn, will require more energy to heat the water; the buildup of solids will also reduce the life of the hot water heating tank.  For this reason, it is more economical to remove hardness from water where hardness is greater than about 120 mg/L as calcium carbonate (7 grains of hardness). Many people argue that hard water for cold domestic use should be softened; they state that hard water will clog pipes, create spots on glass shower doors, and react with soap so that it will not lather.  These are debatable arguments.  Even in locations with very high hardness (300 to 500 mg/L as calcium carbonate or 17.5 to 30 grains), cold un-softened water does not typically cause these severe problems.  Older residences in those locations only use softened water for the hot water system.  It is only recently, with modern plumbing practices, that cold water is also softened.

Determining Type of Water Treatment System

When specific contaminants have been identified in the water, then the proper contaminant removal technique can be selected.  The proper technique is the one that removes all contaminants of concern at the highest efficiency for the lowest financial and environmental costs.  Below are descriptions of common on-site treatment techniques.

Activated carbon filters

Activated carbon is carbon, typically from charcoal, that has been processed to make it very porous.  The more pores in the carbon, the higher the surface area.  The higher the surface area, the more specific contaminants can be pulled from the water to adhere to the carbon, a process called “adsorption”.

Different chemicals have different attractions to the carbon.  For example, heavier compounds have a greater attraction than lighter compounds.   This means carbon filters will not remove every type of contaminant.  In addition, the carbon can become saturated with contaminants and stop removing them.  Most importantly, just before the saturation point, the concentration of contaminants in the water flowing out of the filter begins increasing at a rapid rate.   Therefore, a carbon filter must be removed before the “breakpoint” of the least adsorptive contaminant or else the consumer will be drinking high levels of the contaminant that they intended to remove.  Filter manufacturers make assumptions as to what contaminants might typically be in water and set a common time when filters should be changed.   This may or may not be applicable in individual water systems.

Some carbon filters, such as certain ones that attach to sink faucets, are manufactured so that they combine treatment techniques within a small block of carbon.  Like other activated carbon filters, they have their limitations as to what contaminants can be treated and for how long.  In addition, the filters, themselves, can add contaminants to the water, based on compounds in the manufactured filter material.   There are research projects looking into this phenomenon.

Reverse osmosis and other membrane technologies

Reverse osmosis is a treatment technique that places a membrane barrier in the water.  The membrane is made of synthetic organic materials that do not have straight-through pores like a filter.  Instead, the pores are like a microscopic maze that can prevent many dissolved contaminants from passing through.  High pressure on the upstream side pushes the water, minus many of the contaminants, through the membrane.

There are other membrane technologies where the pores are straighter but very small.  Those technologies remove specific contaminants at lower pressures than reverse osmosis.

Membrane technologies prevent a percentage of the incoming water from going through the membrane, and instead, the water is sent down the drain to waste with the rejected contaminants.  The technique is not practical when it is too expensive to waste a percentage of the available water.  In addition, the synthetic organic membranes can dissolve in contact with some chemicals that might be in the water.  Chlorine used for disinfection is one of the chemicals and it is typically removed in a carbon filter upstream of the membrane.

Physical filters

Physical filters provide a physical barrier that can remove particles from water.  The filters can be made of sand or flossy material that will not allow particles of a certain size to pass through.

Ion exchange/water softeners

Ion exchange is a treatment process where one ion is taken out of the water and others are put into the water in its place.  An ion is an atom or molecule with either additional electrons or missing electrons; this gives the atom or molecule a negative or positive electric charge.   Water softeners are an example of an ion exchange process.  Here, calcium and magnesium, dissolved in the water as positively-charged ions, are “stuck to” negatively-charged ions.  When in contact with the ion exchange material, they are attracted and adhere to the material.  In exchange, the material releases two sodium ions for every calcium or magnesium ion; the sodium ions, then, form a union with the negatively-charged ions that were left behind in the water.  In the case of softening, the sodium concentration increases in the water.

At certain intervals, the ion exchange material must be cleaned to knock off the exchanged ions and replenish the original type of ions on the material.  In the case of water softeners, a solution of sodium chloride (brine) is used to flush out the ion exchange material.  This regeneration process creates a waste stream of chloride-laden water that is sent down the drain and out to the wastewater treatment plant.

Iron and manganese removal

Dissolved iron and manganese in the water eventually react with an oxidant like oxygen or chlorine in the water and precipitate out as a solid on pipe walls, sinks, and laundry.  To remove dissolved iron and manganese before it drops out elsewhere, an oxidant is pumped or bubbled into the water.  After a certain contact time, the iron and manganese are oxidized to a solid form and the particles are filtered out in a sand filter.

The filter must be backwashed periodically to clean the solids out and send them in a waste stream down the drain.

Sequestering

Sequestering is used to hold metals like iron and manganese in the water and prevent them from precipitating out as solids.  Traditionally, polyphosphate chemical products have been used in water systems to hold the metals in the water.  This is especially done when a small water utility or private property owner cannot afford a treatment process to remove iron and manganese.

It is now known that the use of polyphosphates carries negative side effects.  The polyphosphates not only can hold iron and manganese in the water but can also pull lead, copper, and iron from pipes and hold those metals in solution as well.  The consumer drinks any concentration of the metals being held in the water.  Polyphosphates also provide an essential nutrient, phosphorus, for the growth of microorganisms and in doing so, can aid in biofilm formation.  Finally, as the phosphorus from the polyphosphates eventually flows to waste, the wastewater treatment plants struggle with meeting stringent phosphorus discharge limits.

Disinfection

This series of articles on the growth of microorganisms and the formation of biofilms in piping systems has emphasized that disinfection of water is a main weapon against microorganisms.  With a clean piping system, it typically only takes a low dose of disinfection (0.3 to 0.5 mg/L free chlorine) to fight off intruding microorganisms and keep the piping system clean.

When on-site water treatment systems remove or use up disinfection in the incoming water, a dosing system should be added to replenish the disinfection in the water.  For owners of private water sources, continuous disinfection of the water before and after any treatment should be considered.

Some people complain about the taste of chlorine in their water.  If that is in issue, then drinking water can be left in a big pot open to the air or with cheesecloth covering it to allow the chlorine to transfer from the water into the air.  Alternatively, chlorine can be removed by a carbon filter at the drinking water faucet.  (Refer to the carbon filter discussion above.)

A more serious negative effect of disinfection is the possible formation of carcinogenic disinfection by-products.  This can occur when the water has high naturally-occurring organic carbon compounds that react with the chlorine.  If water is received from a municipal water system, disinfection by-products are tracked and minimized by regulation (Table 2); the property owner should re-chlorinate water within the concentration boundaries of the municipal utility.  For private water sources, the owner should become familiar with the disinfection by-product forming potential in the water and chlorinate accordingly.

Determining the Location of the Water Treatment System

Treatment systems located at the point in the plumbing where the water enters the building is called a point-of-entry water system.  Treatment systems located at the drinking water faucet are called point-of-use systems. The location of on-site water treatment in a building’s plumbing system is a critical design decision.

Point-of-entry systems treat the complete water flow to the building and are subsequently larger in size than point-of-use systems.  This creates a greater possibility of biofilm formation in the treatment equipment from increased surface area and retention of water.  It also increases the volume of water needed to clean and maintain the treatment system.  Many point-of-entry systems remove or use up incoming disinfection and so all of the piping downstream of the treatment system is not protected from the growth of microorganisms unless a disinfection dosing system is added.

Although smaller with little or no waste streams, point-of-use treatment systems must be installed for every drinking water faucet, while point-of-entry systems are installed at one location only.

Water treatment equipment for specific needs, such as water softeners for hot water, should be located as close to the specific need as possible.  Water softeners are typically located in a mechanical room adjacent to the water heating system.

Sizing Water Treatment Equipment

The goal of proper modern plumbing design should be to minimize volume of water retained and surface area of the treatment equipment.  The larger the size of the water treatment equipment, the more volume of water is retained on-site and the more surface area is available for biofilm formation.    As already discussed, one way to minimize volume is to eliminate treatment equipment unless absolutely necessary.  In addition, the volume of water to be treated should be carefully considered.  Divide the estimated total water use into: water for drinking/cooking, water for cleaning, and water for any significant purpose such as filling large bathtubs.  Design separate pipelines and treatment strategies for each purpose.

Cleaning Water Treatment Equipment

Various types of water treatment systems have cleaning cycles.  Sand filters must be backwashed to remove trapped solids.  Ion exchange material must be backwashed to remove solids and must be regenerated to replace ions.  Water treatment of this type has automatic clean-in-place cycles.  The cleaning water can be chlorinated to disinfect and fight developing biofilms routinely.  It is critical to work with the equipment manufacturer in setting up a cleaning water disinfection system; chlorine in too high a dose can destroy the treatment material.

Filters that require replacement of filter cartridges should be changed before or at the time recommended by the manufacturer to prevent breakthrough of contaminants and the development of biofilms.

Summary

This article continues the series warning against the growth of microorganisms and the formation of biofilms in plumbing systems.  On-site water treatment systems can contribute to the growth of microorganisms by increasing  the retention time of water, increasing the surface area where biofilms can form, and by removing or using up disinfection in the water.

The first step in plumbing system design is to determine which contaminants in the water are essential to remove on-site.  In many buildings that receive municipal water, additional water treatment is not necessary.  There is a greater need for on-site water treatment when the building is served by a private water source where the property owner must manage their own personal water utility.  There are also special needs for water treatment such as the need to soften hard water before it enters a hot water heating system.

After it is determined what contaminants must be removed, the best removal system must be selected.  Every treatment system has advantages and disadvantages and has specific removal efficiencies for each individual contaminant.   The sizing of the water treatment equipment and its location in the plumbing system are also critical design choices affecting the growth of microorganisms.

Finally, all water treatment equipment must be cleaned and disinfected or filter cartridges replaced routinely to clean out and prevent the formation of biofilms.

Maintaining a high water quality, including the elimination of microbiological growth, is a very delicate balancing act that should be given the highest priority when designing a plumbing system.

Thermal Expansion
by Rich Grimes

We have covered several topics related to water heating in previous articles and we will continue with the issue of Thermal Expansion. Thermal Expansion will occur whenever there is a heat source and the piping loop is “Closed”. This implies that the piping is operating as a Closed Loop, separated from incoming fresh water by a check valve of a backflow device. Closed Loop systems typically operate at lower system pressures than incoming cold water pressures. A closed loop heating boiler is a good example of such a system. The water in the closed loop of piping is not potable and must be prevented from backflow into the domestic cold water supply. Once a backflow device is installed and the loop is heated, thermal expansion will occur and must be controlled. This is also an issue on domestic water heaters installed on “Open Loop” piping because of code required BFP devices.

 

HISTORY

Hydronic heating boilers have always required an expansion tank and the sizing is calculated to absorb the system’s thermal expansion. Water heaters were traditionally installed with no check valve on the cold water supply, so the cold water piping would absorb the expanding heated water. Larger commercial systems would utilize a swing check valve to prevent over-heating of the cold water supply. Plain steel expansion tanks could not be used on fresh water systems so the common practice was to drill a ¼” hole in the flapper of the check valve to allow expanding hot water to escape into the cold water supply. This sounds crazy but it was documented in various manufacturer’s literature and did help to alleviate the problem. But it did not fix the problem.

But along came Backflow Prevention and it created an immediate need for Domestic Thermal Expansion Control. The basis of BFP is to prevent cross contamination, but the result was a “Closed” piping loop that experienced thermal expansion just like a boiler! This is similar to Newton’s Law because for each and every action there is an equal and opposite reaction. All of a sudden there were expansion issues that did not exist before!

Manufacturers of expansion tanks provided tanks with internal bladders that could be pressurized and separated the steel tank from the fresh water. The same tank design was being used on fresh water well systems.

Today, backflow prevention is a standard installation practice on domestic cold water systems. There are various BFP’s and Thermal Expansion devices that can be used, depending on local code requirements.

 

PRINCIPLE

Water cannot be compressed like air so it will expand, creating more volume. This expansion creates a pressure increase that can be entrapped by a check valve or BFP. Water will expand at a rate of .000023 percent for each degree of temperature rise. This may not seem like a lot but if a 30 gallon water heater was heated from 60ºF to 140ºF (80ºF Rise) it would increase in volume by .55 gallons. The additional ½ gallon of water must expand as the volume increases. If there is not a means of expansion control then the expanding water will lift the relief valve to discharge the additional volume and increasing pressure. Temperature and Pressure Relief Valves will discharge with a condition of 210ºF or 150 Psi. Expanding water can easily exceed the 150 Psi T&P valve rating when heating up a “closed” water heater. This is commonly seen at the end of the heating cycle when the relief valve lifts for several seconds. It is also commonly misdiagnosed as a bad relief valve and the replacement relief valve functions just like the “defective” valve, discharging water.

Expansion is a predominately a pressure issue, but temperature accelerates the expansion. Thermal Expansion, expansion caused by heating. New water heaters have a clean heating surface and can expose thermal expansion where the old heater did not display such signs. I have also seen where houses with ½” piping experience more expansion issues than houses piped in ¾”. This is due to the same rate of volume increase with less piping to absorb the expansion. Old heaters that are full of scale have an extended, slower heating cycle that helps to gradually add the expansion.

This will also make you realize how much expansion can be created by large commercial systems with high BTU inputs.

 

THERMAL EXPANSION TANKS

Domestic Thermal Expansion tanks are constructed typically of an epoxy coated steel shell. They have a butyl rubber internal bladder that separates the bare steel from the fresh water. They have a connection for connecting to the cold water supply and an air connection for pre-charging the bladder pressure. The bladder pressure MUST be preset equal to or a little greater than the incoming cold water pressure. This is crucial to installing an expansion tank. A setting of 10 Psi greater than measured cold water pressure is recommended to compensate for varying pressures. For instance, a neighborhood typically has a little less pressure in the morning (heavy use time) than it might at 2:00 PM when the water usage is less. Cold water pressure should be measured with a hose bibb pressure gauge or similar dial-type gauge. Almost every expansion tank comes factory pre-charged to 40 Psi. While 40 Psi may be expected on a well system, pressures of 60 to 80 Psi are common in Florida. A tank that is pre-charged to 40 Psi and is installed on a 60 Psi system will be ineffective. The air in the bladder is pushed all the way up into the tank and it cannot absorb any expansion. An expansion tank must be pre-charged with no water pressure present for the proper setting.

The connection of the expansion tank to the cold water supply is also critical. The expansion tank MUST be installed between the heater and the cold water check valve or BFP. The hot water will try to expand away from the heater towards the cold supply where it is absorbed by the Expansion Tank.

Bladder style expansion tanks can be mounted in the most convenient location and piped over to the system, unlike gravity style tanks which must be located at the highest point of the system. Bladder tanks are also smaller in size to an open gravity tank due to their ability to absorb expansion at a higher volume.

Thermal expansion tanks are sized based on volume of water, incoming water temperature and pressure, stored water temperature and possibly some pressure and expansion factors. There are various sizing programs available in print and online. There are probably ten to twenty manufacturers of domestic thermal expansion tanks to choose from. There are also larger bladder type tanks available for commercial applications.

 

SUMMARY

Domestic Thermal Expansion Tanks are required in most systems today due to backflow prevention devices. These devices provide a solid, positive shut off that will not allow for any thermal expansion. There are also other means of expansion relief, but most involve a self-seating valve that will lift and allow the relief of the additional volume, prior to the heater T & P valve lifting. The Bladder type tanks provide proper expansion protection and also a little protection from water hammer and thermal shock. Systems that experience extreme hammer or thermal shock should be provided with additional protection such as water hammer arrestors or shock absorbers.

It is important to pre-charge the expansion tank and make sure that the connection to the system is located between the water heater and the check valve/BFP. If a tank is existing and has the incorrect pre-charge air pressure, the cold water pressure must be relieved so the tank air pressure can be properly set. Thermal Expansion tanks will prolong the life of water heaters as they absorb the excess volume created by thermal expansion. Backflow prevention is primary to keeping our water supplies safe from cross connection contamination. This technology has created the need for domestic thermal expansion devices that are here to stay.

Thanks and we’ll see you in the next article!

Sincerely,

Rich Grimes

Relaxing at Home
By Sheryl Long

It’s a simple fact that people are spending more time at home and there are many reasons why. Some are directly related to a downturn in the economy. Some are simply the results of people realizing the benefits their immediate surroundings can bring to their life. Cocooning and nesting are terms used in the past for this phenomenon. And in 2009, “staycation” actually made it into the Miriam Webster Dictionary. Whatever you name it, the opportunity is there to promote and sell the amenities that enhance this trend, many of which natural gas can provide.

Entertaining at home lets people enjoy the company of friends and family without driving to a destination. It’s easier to mingle and talk when not confined to a restaurant table. Whether it’s a Sunday morning brunch for four or a cookout for 20, cooking at home keeps the cost dining together manageable so folks can do it more often.

Vacations spent at home let families truly enjoy all that their home and surroundings have to offer. Swimming in the pool every day, taking long hot soaks in the tub, reading a book, and visiting the local zoo and art museum are just some of the many available pastimes. Foregoing a pleasure destination can be the result of a shortage of money or a just a desire to make life simpler, but it doesn’t mean giving up a relaxing and fun vacation time.

Whatever the reason, trends of staying put have homeowners expanding their current space and/or updating kitchens, baths and patio areas, turning their homes into refuges where they want to spend more time. They get to immediately enjoy the comforts of these improvements, and if and when they eventually decide to sell their home, their property value has been increased.

Coach your staff on how to sell this idea of at-home comfort, and you can increase your revenue stream. The opportunities are endless.

Bathroom Spas

In any home, a peaceful, serene bathroom can be a haven. A spa-like atmosphere can be accomplished with large tubs with jets and rain showers. Towel warmers, mirror defoggers and underfloor heat all add to a restful, luxurious retreat.

Natural gas adds a major comfort factor in all of these applications. “Having enough hot water to fill an extra large tub or last through a long shower with a sunflower showerhead is a snap with a natural gas tankless water heater” said Larry Jackson, manager of Partner Development for TECO Peoples Gas. “With a tankless unit there will always be enough hot water. Many homeowners don’t realize their standard water heater won’t suffice.”  Also, natural gas hydro-heat systems can be piped to provide radiant heating of tile floors, mirror defogging and towel warming, adding even more comforts for the client and more revenue for your business.

Fireplaces

Nothing says cozy and homey more than a fireplace in the fall and winter months. Visions of family and friends gathered before a blazing fireplace in the living or family room conjure up good times and memories. However, fireplaces can lend ambience and warmth to any room of the home. A new trend is adding a fireplace in a master bedroom or master bathroom for the ultimate in luxury.

Nowadays, it’s easier than ever for homeowners to get this cozy addition into their house. Natural gas fireplaces offer downhome comfort all at the touch of a button, plus cleanliness and efficiency as well. Stand alone units range from European modern to traditional in style. The new cyclone flames are a look that can make a showcase of any home. Traditional gas fire logs are also available to make converting an existing wood fireplace a simpler project. Vented and vent-free fireplace and log models are available. Look for these additional fireplace opportunities when making service calls. When you calculate the number feet of pipe needed, plus necessary connections and your markup on the unit and installation, the margin adds up quickly.

Kitchen Improvements

For people who love to cook and entertain, the stove or range is almost always at the heart of their kitchen. Upgrading to a professional grade natural gas range can be a dream come true for a serious cook. Other improvement opportunities include adding a built-in natural gas oven or a special water faucet over the stove for conveniently filling large pasta pots, etc. Kitchen remodel piping and appliance sales can boost your bottom line.

Outdoor Living

Particularly in states like Florida where the weather is agreeable most of the year, entertaining outside continues to grow in popularity. Homeowners are building decks and stone patios with outdoor kitchens complete with large, permanently-installed grills, refrigerators and work areas. They’re installing luxurious outdoor fireplaces or firepits to extend the season and adding ambient outdoor lighting to extend the evening. They’re even installing televisions, stereos and artwork specially made to be weather-proof. And don’t forget hot tubs, spas and swimming pools.

Once again, outdoor living provides many opportunities to install piping, connections and appliances. Natural gas products have many benefits for your customers. Grills and cooktops are clean, dependable and fast and easy to use. Outdoor lighting adds a warm soft glow without attracting insects. Patio heaters, fire pits, spa and pool heaters let homeowners enjoy the outdoors year round.

Consider the opportunity for revenue on a summer kitchen. It can include approximately 50 feet of piping to a grill, the gas connection and 75-100 feet of water pipe to the sink. Add a small tankless water heater that’s easily added in an outside installation. Your mark up on these materials and labor can be substantial.

However your customers decide to relax, natural gas amenities can play a part. Don’t forget about the gas piping, appliance installations and connections that can result.