We are back with another article and this time we will look at water quality and its effect on water heaters and boilers.

BOILERS

Boilers are typically closed loop systems where fresh water is used to fill the system but the same fluid is used over and over again. After a system fill, very small amounts of fresh water will enter to maintain system pressure. Chemicals are added to inhibit corrosion and prevent freezing. The dissolved oxygen, calcium and other minerals will precipitate or “fall out” of the heating fluid. They only become present if fresh water is allowed to re-enter the closed loop system.

For instance, I experienced a scaled up heat exchanger on a properly installed closed loop boiler. After further inspection of the closed loop fluid it was found to be untreated fresh water.  The maintenance crew had been using a boiler drain valve to extract heating hot water for cleaning purposes. This occurred every day where they would fill a 5-gallon bucket twice a day. They had access to a Domestic water heating system (right next to the boiler) that resolved their boiler scaling issue.

WATER HEATERS

Water heaters are designed to heat volumes of fresh water up to temperature for domestic and potable uses. The fresh water can contain various minerals and chemicals that will shorten heater life or cause adverse conditions when heated.

Scale build-up is the single most cause of water heater failure and loss of efficiency. The nature of water heater design can be a definitive factor in longevity and overall efficiency but the water conditions are area, utility or site specific. Calcium is present in water and it wants to stick to heating surfaces as it changes from suspension to solids.

ANODE ROD PROTECTION

Most tank-type water heaters use a ceramic porcelain Glass lining to protect the steel vessel interior from fresh water. The glass lining requires a sacrificial anode to cover and protect any weak spots on the lining. Electrolysis will attack the weakest spot on the lined tank interior and the anode is designed to give itself up to fill that particular spot. Over the life of the heater the anode will sacrifice or “give up” small amounts of its soft metal to protect the lining.

The two metals most commonly used in water heaters for anodes are either Magnesium or Aluminum. These metals are softer than steel and less noble. They can sacrifice themselves prematurely if attacked by the content of the water. These have distinct signs and smells that help to recognize how to deal with such issues.

Here are some common water problems related to water heaters and anode rods:

Hydrogen Sulfide – reaction created by a sulfate-reducing bacteria. It occurs with water that has high sulfur content and it attacks the magnesium anode. It is referred to as “Rotten Egg” smell. Hydrogen Sulfide gas in large quantities can be toxic and explosive.

Hydrogen Sulfide normally can be corrected by changing to an aluminum anode rod after performing a complete chlorination and flush of the tank and piping to kill the bacteria. Some manufacturers specifically use an aluminum anode rod as standard equipment in Florida to avoid the reaction to magnesium.

Aluminum Hydroxide – reaction caused by high pH water. It occurs many times in areas with high chlorine/chloramines in the water supply. Chlorine has a very high pH of 11.7. This reaction forms a jelly-like substance on the anode rod and in the bottom of the tank. It can appear as grey, blue or green beads or gel. The odor produced smells something like week-old trash so it is not something you can tolerate very long!

High pH also means alkaline or scaling so the tank must be flushed out and possibly de-scaled. The reaction is treated with the other viable anode made of magnesium.

Water Softeners – water softeners reduce grains of hardness through a process of ion exchange. Most water softeners exchange sodium (salt) ions with insoluble calcium and magnesium ions. Sodium can increase electrical conductivity and accelerate anode consumption. Use of water softeners warrant monitoring of pH level, conductivity and anode inspection at a regular interval, no less than once a year.

Stagnation – allowing the same water to exist in the tank for long periods of time will result in stagnation. The potential for bacteria increases. This can attack the anode and the results are smelly water and a heater that needs service. Many seasonal residents of Florida will leave their winter homes and forget to drain down their water heater. They typically turn off the power before they leave and the low temperature, stagnated water starts creating the perfect Petri dish. The other application is a larger storage heater that does not get used much, where very little fresh water enters to replenish the stagnated water. A 50 gallon heater on a break room sink is a great example of an over-sized and under-used heater.

Grounding – bad earth grounding can create an electrical potential that will erode the anode at a rapid rate. Once the anode is gone, the steel tank is attacked by the electrolysis.

NEW ANODE TECHNOLOGY

There is newer technology on water heaters for cathodic protection. Electronic controls can help to implement a non-sacrificial anode. The benefits of such a device are a milestone in tank protection.

The Powered Anode is a titanium rod that is immersed in the top of the heater tank. It can function as a Low Water Cut Off to insure that the tank is full of water. Titanium is a very hard metal, mostly impervious to fresh water and much more noble than steel. It will last longer than the water heater and does not sacrifice itself. So there is no smell that will be generated by this non-sacrificial anode rod.

The electronic controller will send out a micro-DC current to the Titanium rod to offset electrolysis. The electronic controller sends out more micro-DC voltage as the tank lining gets older. At some point, the electronic control cannot put out any more current. The integrity of the tank lining is so diminished it is already leaking or within days or weeks of leaking. This is a valuable feature, to know that when you cannot maintain power to the electronic anode rod, you are about to experience a tank failure in the very near future. Time to schedule a change out!

OTHER WATER ISSUES

Water can and will contain a variety of chemicals and minerals that can create adverse conditions when heated. The heating of the water will increase precipitation of scale. It causes the calcium to leave solution form and become a solid that sticks to itself and accumulates on heating surfaces.

High iron content is very common in Florida with well systems. Tannic acids will turn the water yellow to brown in color. Lime is naturally present in every water source to some degree. Bacteria can also be thriving in a particular water supply. The process of heating accelerates the various reactions. There is a wide range of targeted treatment and filtration products that can address these such as UV, Iron filters and the like.

It is important to remember that it is not the fault of the water heater, but a adverse reaction to the water…

Keeping Plumbing system free of microorganisms
by Abigail Cantor, P.E. (Chemical Engineer)

This is the third article in a series about the possibility of microorganisms growing in plumbing systems.  The first article warned that with high residence time, high surface area, and no disinfection, microorganisms can grow out-of-control in plumbing systems.  The second article provided a tour of a plumbing system, pointing out where and why microorganisms are likely to grow.

This article describes three actions that can prevent microorganisms from growing out-of-control in a plumbing system:

1. Flushing
2. Disinfecting
3. Monitoring

Flushing Pipes

Unfortunately, while flushing of pipes with fresh water will keep the population of microorganisms down, it is not always practical for plumbing systems in buildings.  Flushing requires a large quantity of water, especially for buildings with a long, complicated piping system and a large volume of hot water storage.

In addition, a high velocity of water is required to remove biofilms from pipe walls once they are attached.  It may be impossible to reach these cleansing velocities if pipe diameter and tank volumes in the plumbing system are large or the water pressure is too low.  A high velocity, also, cannot be maintained in the multiple bends and branches of a building’s plumbing system.  Even if a scouring velocity can be achieved, some biofilms continue to adhere firmly to pipe walls.

Table 1 shows the flow rate of water required to achieve a flushing and scouring velocity of 6 feet per second.

Table 1.  Flow Rates of Water at a Scouring Velocity of 6 Feet per Second

Notes:

1. 1.     This table uses the internal diameter of Type L copper pipe
2. 2.     Flow Rate = Velocity x Cross-Sectional Area of Pipe
3. 3.     Unit conversion used in calculation: 12 inches = 1 foot
4. 4.     Unit conversion in calculation: 448.8 cubic feet per second (cfs) = 1 gallon per minute (gpm)

Disinfecting Water

An alternative to flushing with a large volume or a high velocity of water is flushing with a low volume of disinfected water.   There are a number of types of disinfecting chemicals that can be used, but a common chemical for drinking water is sodium hypochlorite which provides chlorine as the active disinfecting ingredient.  Another name for sodium hypochlorite is bleach, which can be purchased at grocery and hardware stores.  It is important to purchase household bleach that has no additives along with the sodium hypochlorite.  In household bleach, about 5.7% of the product is active chlorine.  Even though this sounds like a small amount, the concentration of active chlorine in the bleach is very high —   about 62,700 mg/L chlorine.

Many municipal and community water systems use liquid sodium hypochlorite or gaseous chlorine to disinfect the drinking water before it enters the distribution system.  Enough chlorine is added to maintain a disinfecting concentration all the way to the farthest locations in the distribution system.  Disinfecting in a building that receives chlorinated drinking water would boost the existing chlorine concentration or replenish the chlorine concentration after on-site water treatment devices have removed the municipal disinfection.

Some municipal water systems use a combination of chlorine and ammonia to create monochloramine for disinfection.  Monochloramine is not as strong a disinfectant as chlorine and must be used at a higher concentration to achieve a similar disinfecting power as free chlorine.  In a building that receives chloraminated drinking water, household bleach can still be used for boosting or replenishing disinfection.  However, if monochloramine or ammonia is present in the water, it will take more bleach to reach the desired active chlorine concentration than if only chlorine was present.

Active chlorine is referred to as “free” chlorine because it is not combined with other chemicals and is available to react with microorganisms.  “Total” chlorine refers to free chlorine plus chemical compounds where chlorine is combined with other chemicals.  When disinfecting with sodium hypochlorite, the concentration of free chlorine is a measure of disinfecting power.  When disinfecting with monochloramine, total chlorine is used to estimate the disinfecting power because chlorine is combined with ammonia, but the measurement of total chlorine also includes any free chlorine and any other compounds of chlorine that have formed in the water.  A better measure of disinfection power, in this case, is to directly measure monochloramine concentration.  However, the Total Chlorine test kit is more widely used as a convenience.

If it is desired to boost or replenish chlorine in a plumbing system, chemical injection equipment is needed.  Chemical injection equipment consists of a chemical feed pump with accessory valves for proper operation (Figure 1).  A multi-function valve, typically purchased with a chemical feed pump, provides for venting of air trapped in the suction line, pressure release, provision of required backpressure, and prevention of siphoning.  A foot valve at the end of the suction tubing in the chemical storage tank prevents backflow of chemical solution from the tubing back into the tank.  A chemical injector is a device with a ball check valve that connects into a threaded tee in the main pipeline and allows only forward flow of the chemical into the drinking water pipeline.  Additionally, a pulsation dampener and/or a static mixer (a pipe section with interior vanes) may be necessary for proper mixing of the chemical into the drinking water.  Automatic control of the chemical feed pump can be added by using a flow meter in the drinking water pipeline that sends an electric signal to the chemical feed pump to dose the chemical based on flow of the water.

Figure 1.  Typical Chemical Injection Equipment

To maintain disinfection throughout a plumbing system, sodium hypochlorite can be injected at critical locations where disinfection needs boosting or replenishing.  The article, “Critical Locations for Microbiological Growth in Plumbing Systems” explains that those locations are typically after certain water treatment devices.  For buildings fed by private wells, disinfection is also needed in the well water as it is discharged from the well pump.  Refer to the article for more detailed information as every plumbing system should be assessed individually for disinfection needs.

Care must be taken in selecting a proper dosage of chlorine for disinfecting plumbing systems.  Federal drinking water regulations demand that free chlorine concentration stay below 4 mg/L.  Many municipal and community water systems maintain a free chlorine concentration between 0.2 and 0.5 mg/L in the distribution system.  Some systems may go up to 1 mg/L.  Dosage of monochloramine in municipal water systems is typically between 1 and 3 mg/L total chlorine.  See Table 2 for a summary of typical disinfection concentrations.

Table 2.  Typical Disinfection Concentrations

Chlorine can break down plastic components used in modern plumbing systems.  There is not well-documented information on the chemical compatibility of various plastics and chlorine, but when asked, many manufacturers of plastic components that come in contact with drinking water cite the drinking water regulation of 4 mg/L maximum.  However, the more exposure to higher chlorine concentrations over time, the shorter the life of the plastic components, so it is better to stay below 1 mg/L free chlorine.

Resin beads inside water softeners and ion exchange water treatment devices also break down over time in contact with higher chlorine concentrations.  Manufacturers will allow the resin to come in contact with 1 mg/L free chlorine for short time periods, but staying in the lower 0.2 to 0.5 mg/L range is better for the life of the beads.

The maximum allowable chlorine concentration in hot water systems is not known.  The higher temperatures push the chlorine to be more reactive and there is danger that the chlorine can corrode metals.  It is best to stay closer to 0.1 to 0.3 mg/L.

As was noted previously, the concentration of chlorine in household bleach is very high so only a small quantity of bleach is added to water to achieve free chlorine concentrations found in drinking water.  Table 3 lists the amount of bleach that should be added to water to reach drinkable concentrations.

Table 3.  Free Chlorine Concentrations and Volumes of Household Bleach (5.7% active chlorine) in 100 Gallons of Water

Note:   To measure milliliters (mL) of bleach, purchase a container marked in milliliters, called a “graduated cylinder”, from a laboratory supply company.  Graduated cylinders come in various sizes with various precision of measurement, such as a 10 mL cylinder marked in gradations of 0.2 mL or a 25 mL cylinder marked in gradations of 0.5 mL.

Monitoring Water Quality

To prevent the growth of microorganisms in pipes, the goal is to provide just enough fresh water and just enough disinfection to continuously expose the pipes to a minimum of about 0.3 mg/L free chlorine in the water. Routine monitoring of chlorine concentrations throughout the plumbing system is necessary to determine if the pipes are getting the proper exposure to disinfected water.

Field test kits are available for measuring chlorine concentrations in water.  An example of a field test kit is the Pocket Colorimeter™ II from the Hach Company.  The test kit can measure both free and total chlorine concentration.  With sodium hypochlorite disinfection, free chlorine concentration should be measured.   With chloramine disinfection, total chlorine concentration should be measured as an estimate of monochloramine concentration.  The instructions for measuring the chlorine concentration come with the field test kit and are simple to follow.  These are relatively inexpensive, simple, and convenient tests that can routinely guide flushing and disinfection dosing in piping systems.

Unfortunately, the control of microorganisms is a little more complicated than merely maintaining a specific disinfection concentration.  The conditions in piping systems and water environments vary and microorganisms can still grow at disinfection concentrations that are typically effective elsewhere.  Monitoring of “microbiological activity” should be performed in addition to monitoring disinfection concentration.

The best method of monitoring for microbiological activity has not been determined at this time.  However, one test is typically used to estimate microbiological activity.  It is called Heterotrophic Plate Count (HPC).  The test should be performed by a commercial laboratory that uses a special nutrient in the incubation dish called R2A.  There are many laboratories that will perform an HPC test, but not all will use the R2A. Table 4 lists the criteria that the laboratory should use to run the test.   The tests are about $30 a sample but overnight transport to the laboratory should be considered in the overall cost. After finding a laboratory that performs these tests according to the criteria listed in Table 4, have the laboratory send sample bottles for HPC_R2A sampling in disinfected water.  To take HPC_R2A water samples from a plumbing system, the water in the plumbing system must sit stagnant for a minimum of six hours.  It is good to use a similar stagnation time each time.  When it is time to take samples, wipe the faucet or sample tap opening inside and out with an alcohol wipe, wiping off any excess alcohol.  Open the sample bottle carefully because it has been sterilized to prevent contamination of the water sample.  Do not touch the inside of the bottle, the rim of the bottle, or the inside of the cap.  Capture the first-draw stagnation water in the sample bottle and fill the bottle to the indicated line.  Cap and label the sample bottle.  Put the bottle on ice in a cooler and get the sample to the laboratory within twenty-four hours.

Table 4.  Laboratory Requirements for the HPC_R2A Water Analysis

There is another test that has been found to be a better measure of microbiological activity than HPC.  It is a test that measures chemical compounds of metabolism (ATP) for organisms in the water.  A second generation method has been developed but is not readily available at this time in water testing laboratories.

Summary

Flushing of pipelines and disinfection of water are the available tools for preventing out-of-control microbiological growth in plumbing systems.  In order to determine the right amount of flushing balanced with the right amount of disinfection, water quality throughout the plumbing system must be monitored routinely.

This article describes the details of flushing and disinfecting plumbing systems and testing for chlorine and microbiological activity.  Future articles will use this information to suggest a practical approach for building and plumbing contractors for preventing out-of-control microbiological growth in modern plumbing systems.