Design Requirements for a Water Distribution System in a ...

Philip Andrysiak, BS, MBA, CHT; Philip M. Varughese, BS, CHTDesign Requirements for aWater Distribution Systemin a Hemodialysis CenterWater systems are an integral part of the dialysis facility. They are vital to the safe and effectivetreatment of the patient. There are a variety of components used to supply water to eachdialysis machine. Part of this system of components is the piping used to distribute this water.There are specific flow velocities required that minimize bacterial adhesion to the piping system.The purpose of this article is to help with the design of a water distribution system thatwill maintain adequate flow velocities throughout the entire system. This article presents a newapproach toward designing the water distribution system for the hemodialysis center.This educational article has been especially designed to provide one (1) contact hour (CH)credit for registered nurses (RNs), Patient Care Technicians (PCTs), Biomedical and EquipmentTechnicians, and other direct-care personnel who are licensed and certified by theBoard of Registered Nursing (BRN) of California. Most (not all) American states recognizeand accept the California BRN-certified CHs. Thus, most American healthcare personnel canreceive CHs—which are applicable for recertification or relicensure—from reading this articleand then answering a post-test (see sidebar). There is no charge to receive the CH credit.It is the reader’s responsibility to contact his/her BRN, its equivalent, or other certifyingbodies prior to submitting this post-test for CH credits to determine acceptability by thereader’s state and/or certifying agency.1.0 CONTACT HOURSObjectives• To determine the different flow velocities needed in direct and indirect water feed systems.• To determine the minimum flow velocity needed in a dialysis facility.• To understand the reason for having a specific flow velocity.• To understand the quality of water needed in a dialysis facility.• To be able to specify the correct materials for use in a dialysis facility’s water distributionsystem, and to specify those materials that are not appropriate.• To understand those factors that affect the flow velocity in the water distribution system.• To be able to calculate the flow velocity at any point in a dialysis facility.Philip Andrysiakis a Renal Consultantbased in Homestead,Florida. Philip M.Varughese is FacilityAdministrator, DaVita-Richmond Kidney Center,Staten Island, New York.Ever since the early days of dialysis,transporting water has been one ofthe many challenges faced. From theoriginal batch systems with 120 L of solution,to the current single-patient deliverysystems that require up to 1,000 ml perminute, delivering quality water to the patients’treatment area is still a challenge.Water systems are an integral part of anyhemodialysis facility. There are various mechanicalcomponents—from the pretreatment,to the reverse osmosis (RO), to the post-treatment—thatare used to provide the properquality water for the dialysis treatment. Onceit passes through the purification process, thewater needs to be distributed to the dialysisequipment. There are certain requirements fordistributing water to each individual station(dialysis machine, reprocessing equipment,bicarbonate filling area, etc.), as well as manydrawbacks with delivering this large a quantityof water.OCTOBER 2002 VOLUME 31, NUMBER 10 DIALYSIS & TRANSPLANTATION 683

WATER DISTRIBUTION DESIGNOn the surface, it might appear tobe relatively easy to supply water toeach individual station. However, thereare requirements that need to be met inorder to ensure a safe water quality.Each station requires a specific waterflow rate, along with a minimumand maximum pressure. If only theminimum pressure and flow rate weresupplied, the result would be a verylow flow velocity. There would evenbe areas within the supply system thatwere completely stagnant; this is especiallytrue with a direct distributionsystem (no storage tank). Therefore, itis imperative to build in extra flow capacityabove what is needed, creatinga “scrubbing” velocity. Along withroutine disinfection, this will aid inpreventing bacterial adhesion that canlead to biofilm and its consequentproblems. For this reason, there areminimum flow requirements.Loop Flow DesignBoth with indirect (storage tank) anddirect feed systems, the water shouldflow in a loop. This means that the watertravels in a continuous circlethroughout the facility without anybranching off. The unused, expensivelypurified water is then returned to eitherthe RO or the storage tank and notdiscarded to drain. Furthermore, witha loop design, along with proper pipingsize, you can achieve higher flowrates through the system, which givehigher flow velocities.Determining the Loop Flow VelocityThe flow rate is described in terms ofcubic feet per minute. This then getsconverted to the flow velocity in feetper second (FPS). For a direct feed system,a minimum flow velocity of 1.5FPS is required, as measured at the“end” of the loop and during peak demand(all systems operating and drawingwater). For indirect feed systems,the minimum flow velocity would be 3FPS, with an average range of 3–6 FPS.If the flow velocity is too high, theremay be excessive noise in the system,as well as excessive heat, not to mentionthe increased wear and tear andelectrical costs of running the pumps atan excessive speed. Consider, however,that in ultrapure applications outside ofdialysis, flow velocities of 8–10 FPSare not uncommon.When designing a system, it is importantto remember that the flow ratewithin the piping system will vary. Itwill be very high at the beginning ofthe system and will decrease as thewater moves through the pipe. The reasonis that the various hemodialysisequipment demands a certain amountof water from the loop as the waterpasses by, decreasing the volume aseach piece of equipment collects its requirement.When designing a systemand loop, it is imperative to take intoaccount the flow requirements of eachindividual hemodialysis machine,piece of reuse equipment, bicarbonatefill station, machine repair station, etc.The water requirements can be calculatedfor the best-case and worstcasescenarios by using theDistribution Loop Flow Analysis depictedin Table I, and which is availableon-line (see sidebar). For example, youcan calculate the flow velocity with thereprocessing equipment either runningor with it off. You can also do the samething with the bicarbonate mixer. Keepin mind that the minimum flow velocityis with everything running.Although in current practice the diameterof the distribution piping isconstant for the entire loop, the flowvelocity can also be maintained by usinga step-down approach. By progressivelydecreasing the size of thepiping, a higher flow velocity can bemaintained for the entire loop. Thiswould also help to maintain consistentpressures throughout the loop. In orderto accurately determine the flow velocity,you will need to know the precisediameter of the pipe, along withthe initial feed flow rate. Installing aflow meter at the end of the loop willallow you to verify that the system hasbeen designed correctly.A word of advice: Build in spaceand options for future expansion ofyour facility so that your brand-newwater system and loop are not obsoletein a few years and so that yourcapital investment is not lost.Water QualityVarious agencies either regulate orrecommend the quality of the waterthat is needed in a dialysis facility.The agencies that regulate the outpatientdialysis facilities are the statehealth departments and the Centersfor Medicare & Medicaid Services(CMS; formerly the Health Care FinancingAdministration [HCFA]).They typically adopt the Associationfor the Advancement of Medical Instrumentation(AAMI) guidelines.AAMI is a volunteer board that recommendspolicies for both manufacturersand end-users alike, and theirguidelines pertaining to water qualityGlossaryFlow Rate is the Volume of water deliveredper unit of time (e.g., gallons per minute)Flow Velocity is the Distance that thewater travels per unit of time (e.g., feetper second)Water Pressure is determined bymultiplying the Flow Rate times theResistance (measured as psi/GPM)offered by the pipeTo convert Liters per minute (LPM) toGallons per minute (GPM), multiply by0.2642To convert GPM to Cubic Feet perminute, multiply by 0.1337To convert GPM to Cubic Feet persecond, divide GPM by 60 and thenmultiply by 0.1337To convert the Pipe Diameter in inchesto the Pipe Radius in feet, divide theInternal Diameter by 2, then divide theresulting number by 12Cross-Sectional Area of the pipe isdetermined by the formula 2πr (2 x 3.14x radius of the pipe)Feet per Second = Cubic Feet per seconddivided by the Cross-Sectional Area684 DIALYSIS & TRANSPLANTATION OCTOBER 2002

WATER DISTRIBUTION DESIGNfor hemodialysis can be found inthe monograph, ANSI/AAMIRD62:2001. 1,2The AAMI recommendation forbacteria is less than 200 colony formingunits (CFU)/ml for all water usedin dialysis, including the water in thedistribution system, with an action levelof 50 CFU/ml. If 50 CFU/ml is reported,then an action should be takensuch as disinfecting the RO and/orloop and resampling. For endotoxins,the AAMI recommendation is lessthan 2.0 endotoxin units (EU)/ml withan action level of 1.0 EU/ml.The European recommendationsare more stringent. The EuropeanPharmacopoeia suggests a limit of100 CFU/ml for bacteria, with an actionlevel of 25 CFU/ml. For endotoxins,the limit is 0.25 EU/ml, with anaction level of 0.0125 EU/ml.A properly designed water distributionsystem will keep to a minimumthe stagnant areas in the distributionsystem. Along with an aggressive, routinedisinfection of the RO and loop,this should keep the bacterial and endotoxinlevels within an acceptablerange for longer periods of time.EndotoxinsThe challenge for any hemodialysis facilityis to provide water that is endotoxinfree. Bacteria will not cross thedialyzer membrane unless there is amicro leak or unless bacteria are introducedduring the reprocessing stage.Bacteria introduced during reprocessingare killed as a result of exposure tothe disinfectant, but they will leave endotoxinsin their wake.Endotoxins reside in the cell wall ofGram-negative waterborne bacteria.When the bacteria die, they releasethese toxins. Endotoxins can cause pyrogenicreactions in patients (feverspikes, chills, myalgia, nausea andvomiting, hypotension). Pyrogenic orendotoxin reactions typically occur inmore than one patient in a given dialysisfacility at a time. They also usuallyoccur at 1 hour to halfway into thetreatment, though they may occur earlierdepending upon the amount of endotoxinexposure, dialyzer efficiency,back filtration issues, underlying infectionprocesses in the patients, andendotoxin build-up in the dialyzer as aresult of multiple reuses.In addition to pyrogenic reactions,there are well-documented chronic inflammatorydisease processes that havebeen seen in patients exposed to lowlevels of endotoxins over time; thus,the tighter standards for endotoxins.Reverse osmosis will remove molecules>200 MW, which will encompassalmost 100% of endotoxins.However, in dialysis we are not makingsterile water, and no water loop candeliver water that is bacteria and endotoxinfree. For this reason, it is a goodidea to incorporate an ultrafilter oneach hemodialysis machine prior tothe point where the dialysate enters thehemodialyzer. In this way, you are assuredof dialysate going to the hemodialyzerthat is endotoxin free.Incorporating ultrafilters in thelines leading to the storage tank and inthe water loop will further aid in theprevention of bacteria colonizationwithin the loop. However, these filterswill reduce the flow rate and, therefore,decrease the flow velocity; thus,they have to be carefully thought outand designed into the system. Otherpoints of use that require ultrafiltrationare the reuse equipment and the bicarbonatefilling station. Ultrafilters needto be disinfected and/or replaced on aroutine basis or they will grow bacteriaand shed endotoxin—the very thingsyou are trying to remove!Construction ConsiderationsThe way in which the water distributionsystem is installed is critical andrequires attention to certain details thata local plumber might not understand.Typically, the material of choice in theU.S. is polyvinylchloride (PVC)schedule 80. However, there is somemovement toward more pristine materialssuch as polyvinylidenefluoride(PVDF), polypropylene (PPE), etc.When using these types of specialtypiping, you should assure that the installerunderstands how to correctlyweld the material; otherwise, you mayhave wasted your money.When using PVC, the pipe shouldbe cut using an approved PVC pipe-cuttingmethod (a PVC pipe cutter, for instance,looks like a knife and cuts thepipe square). The pipe should not be cutwith a hacksaw, as this will leave arough edge to which bacteria can adhere.Once the pipe is cut, a chamferingtool should be used that will round offthe inner and outer diameter of the pipe.Chamfering the edges will reduce theburrs, thus allowing the glue to be moreevenly distributed; it will also decreasethe occurrence of stress points so thatthe pipe will be less likely to crack.All solvent welds should be primedprior to the gluing process. Primercomes both with and without a bluetint. If it has a blue tint, the solventweld can be inspected after it has beencompleted. Where possible, all connectionsshould be solvent welded; however,the over-use of glue should beavoided, as the excess glue can hangdown and provide places for bacteria toattach. Threaded joints also should beavoided, as they will have spaces wherethere will be stagnation, thus increasingthe possibility for bacterial growth.Ninety-degree turns in the loopshould be accomplished through theuse of two 45-degree angles. This willprovide a more even flow through theturn and prevent the stagnation thatoccurs when a 90-degree turn is used.The connections to the stationsshould be kept as short as possible. Inthis way, when a station is not in use thestagnant areas will be kept to a minimum.The connection to the stationshould be maintained at as high a flowvelocity as possible. Nonetheless, itwill probably not be possible to achievethe minimum flow velocity of the distributionloop for this short segment.You can, however, achieve the highestpossible flow velocity by using aOCTOBER 2002 DIALYSIS & TRANSPLANTATION 685

686 DIALYSIS & TRANSPLANTATION OCTOBER 2002Table IDistribution Loop Flow AnalysisA B C D E F G H I1 Station LPM GPM Total GPM Cu. Ft./Sec. Pipe Dia. (In.) Pipe Rad (Ft.) Area Ft./Sec.2 FEED 40.00 10.57 10.57 0.0235 0.95 0.0396 0.0049 4.783 1 0.80 0.21 10.36 0.0231 0.95 0.0396 0.0049 4.694 2 0.80 0.21 10.15 0.0226 0.95 0.0396 0.0049 4.595 3 0.80 0.21 9.93 0.0221 0.95 0.0396 0.0049 4.506 4 0.80 0.21 9.72 0.0217 0.95 0.0396 0.0049 4.407 5 0.80 0.21 9.51 0.0212 0.95 0.0396 0.0049 4.308 6 0.80 0.21 9.30 0.0207 0.95 0.0396 0.0049 4.219 7 0.80 0.21 9.09 0.0203 0.95 0.0396 0.0049 4.1110 8 0.80 0.21 8.88 0.0198 0.95 0.0396 0.0049 4.0211 9 0.80 0.21 8.67 0.0193 0.95 0.0396 0.0049 3.9212 10 0.80 0.21 8.45 0.0188 0.95 0.0396 0.0049 3.8313 11 0.80 0.21 8.24 0.0184 0.95 0.0396 0.0049 3.7314 12 0.80 0.21 8.03 0.0179 0.95 0.0396 0.0049 3.6315 13 0.80 0.21 7.82 0.0174 0.95 0.0396 0.0049 3.5416 14 0.80 0.21 7.61 0.0170 0.95 0.0396 0.0049 3.4417 15 0.80 0.21 7.40 0.0165 0.95 0.0396 0.0049 3.3518 16 0.80 0.21 7.19 0.0160 0.95 0.0396 0.0049 3.2519 17 0.80 0.21 6.97 0.0155 0.95 0.0396 0.0049 3.1620 18 0.80 0.21 6.76 0.0151 0.95 0.0396 0.0049 3.0621 19 0.80 0.21 6.55 0.0146 0.95 0.0396 0.0049 2.9622 20 0.80 0.21 6.34 0.0141 0.95 0.0396 0.0049 2.87232425262728293031WATER DISTRIBUTION DESIGN

WATER DISTRIBUTION DESIGNsmaller pipe size for this short segment.By disinfecting the RO, the loop,and all of the machines connected tothe system at the same time, you willbe able to disinfect the connections andthe inlet hoses to the dialysis machines,which are often neglected.The use of any metals in the systemother than a high-grade stainlesssteel (316L) is not appropriate. Othermetals (brass, copper, aluminum) canleach into the water and cause harmto the patient. The materials used inthe system—including O-rings andpump seals—must be compatiblewith the disinfectants used. Nitrilerubber, for example, is not compatiblewith peracetic acid. Where thisdisinfectant is used, the preferred materialwould be a fluorocarbon elastomeror ethylene propylene.Calculating the Flow VelocityThis article provides you with thespreadsheet program needed to calculatethe flow velocity of a dialysiscenter’s water distribution system.The spreadsheet program is availableon-line (see sidebar). An exampleof a completed spreadsheet isshown in Table I. The entries foundin the various columns are the resultof mathematical derivations performedautomatically once key informationis inputted into selectedcells. The net result is the flow velocity,shown in the far-right columnin feet per second.Column A is the station number.Column B is the flow rate in liters perminute. The initial flow rate is entered,and then the flow rate for eachmachine is entered (which is automaticallysubtracted from the initial flowrate). Each station’s flow rate willthen be subsequently subtracted.Column C converts liters per minuteto gallons per minute. This is the gallonsper minute for that specific machine,or for the initial input.Column D is the total gallons perminute after that station.Column E converts first to cubicfeet per minute, and then to cubicfeet per second.Column F is the actual pipediameter in inches.Column G converts the pipe sizefrom inches to feet, and also convertsdiameter to radius.Column H is the cross-sectional areaof the pipe in square feet.Column I is the final answer—theflow velocity—in feet per second. Ittakes the cubic feet per second anddivides it by the area of the pipe.Now you can enter the specifics foryour facility. What you need is the flowat the beginning of the system in litersper minute (LPM) and the flow requirementsof the hemodialysis equipment,dialyzer reprocessing equipment, andbicarbonate mixing station. These willbe entered in column B.You will also need to know the sizeof the pipe in the system. Remember,all pipes will have an actual size thatis different from the stated pipe size.A 1˝ pipe, for instance, will have aninternal diameter of less than 1˝. Thepipe size will be entered in column F.Table I is what a 20-station facilitywould look like with a 40-LPM flow rateinto the beginning of the loop, with hemodialysisequipment that uses 800 mlper minute. By using this method, youcan determine the flow velocity of a systembefore you begin construction. Youwill not have to install a distribution pipingsystem and then measure the flowvelocity; you can determine the flow velocitybefore construction even begins.ConclusionYou can have the best RO system in theworld, but if the loop is poorly designed,or if an old loop is left in place when installinga new water treatment system,you will have a biofilm problem. Remember,too, that if the best-designedwater treatment system and loop are installedyet not properly maintained, youwill still have a biofilm problem.A combination of proper watersystem design coupled with aggressivecleaning and disinfection is yourbest bet against bacteria build-up inthe system.References1. AAMI Standards and Recommended Practicesfor Dialysis. Arlington, VA: Association for theAdvancement of Medical Instrumentation, 2001.2. Luehmann DA, Keshaviah PR, Ward RA,Klein E. Water Treatment for Hemodialysis.Rockville, MD: U.S. Department of Health andHuman Services, Public Health Service, Foodand Drug Administration, Center for Devicesand Radiological Health, 2002.POST-TEST1) Which of the following areappropriate water distributionsystems?a) indirect systemsb) direct systemsc) storage tank systemsd) all of the above2) For a direct feed system, the minimumflow velocity should be:a) 0.5 feet per secondb) 1.0 feet per secondc) 1.5 feet per secondd) 3.0 feet per second3) The minimum flow velocity for asystem should be measured at the:a) beginning of the loopb) middle of the loopc) end of the loopd) at all points of the loop4) The flow velocity in a directOCTOBER 2002 DIALYSIS & TRANSPLANTATION 687

WATER DISTRIBUTION DESIGNfeed system is:a) higher at the beginning ofthe loopb) higher at the end of theloopc) highest at the middle ofthe loopd) the same at all points ofthe loop5) The purpose of maintainingflow velocity in the distributionsystem is to:a) lower endotoxinsb) reduce biofilmc) provide adequateflow to the machinesd) all of the above6) The most common materialfor distribution piping used indialysis is:a) polyvinylchloride (PVC)b) polyvinylidenefluoride(PVDF)c) polypropylene (PPE)d) none of the above7) The material that is unacceptableto use in the distributionsystem is:a) copperb) brassc) galvanized steeld) all of the above8) If the dialysate flow rate of thehemodialysis equipment is increased,the flow velocity will:a) stay the same throughoutthe systemb) be lower at the beginningof the loopc) be lower at the end ofthe loopd) be lower at all points inthe system after the firstmachinee) answers c and d9) A minimum flow velocity inthe distribution system will:a) prevent bacterial adhesionb) prevent endotoxin adhesionc) provide adequate flow tothe hemodialysis equipmentd) answers a and b10) The following will affect theflow velocity in the distributionsystem:a) initial flow rateb) pipe diameterc) hemodialysis equipmentdialysate flow rated) all of the above D&TObtaining Contact HoursThe certifying agent for these contact hours (CHs) isHemodialysis, Inc. (Hi), a Southern Californiahealthcare corporation. Hi—in conjunction withDialysis & Transplantation—makes these CHsavailable as a free perquisite to the readers of thiseducational product. Those healthcare personnelwho wish to receive a certificate for one (1) CH arerequired to correctly answer and submit the 10-questionpost-test that can be found elsewhere in this article.All post-tests for this article must be receivedin Hi’s offices prior to August 16, 2004.Download from the Web: This article and the posttest—aswell as the Excel ® spreadsheet discussedwithin the article—can be downloaded directly fromHi’s Web site: www.Hemodialysis-Inc.com. A linkcan also be found on D&T’s Web site,www.eneph.com. For any specific questions pertainingto the use of the Excel spreadsheet, contactPhilip Andrysiak at PHA160@aol.com.Disclaimer: With few exceptions, other states’ nursingorganizations, as well as other certifying bodies,recognize California Board of Registered Nursing(BRN) CHs. It is the reader’s responsibility to contactthose organizations to verify that they accept CaliforniaBRN CHs. We make no claim or representationthat the earned CHs are applicable outside of California.Since 1998, Hemodialysis, Inc., has publishednursing literature containing CHs. These educationalinstruments have been purchased by dialysis and othernursing personnel in most, if not all, of the 50American states, as well as overseas and in Canada.Letters from purchasers whose state or country doesnot have a BRN nor a requirement for CHs have indicatedthat employers use and value these CHs forthe evaluation of employees for the purposes of promotionand salary enhancement. Thus, these CHshave substantial value even if they cannot be appliedtoward recertification or relicensure.688 DIALYSIS & TRANSPLANTATION OCTOBER 2002

WATER DISTRIBUTION DESIGNPhotocopy, Complete, and Mail This Post-Test Form To:Hemodialysis, Inc.ATTN: Water Distribution System Post-Test1560 E. Chevy Chase Dr., Ste. 435Glendale, CA 91206-4175 (USA)A self-addressed business-size envelope (9˝ x 4 1/4˝) with first-class postage affixed must be enclosed with the post-test.No request for CHs will be processed without this requirement.All Post-Tests for this educational article must be received in Hi’s offices prior to 5:00 p.m., August 16, 2004.For any questions, please call Hemodialysis, Inc., at 818/956-5357.Name (first and last) ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––Street Address (include Apt. #) ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––City, State, Zip Code––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––Home Phone (include Area Code) ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––❒ RN ❒ LVN ❒ PCT ❒ MD ❒ PhD ❒ Other (specify) ––––––––––––––––––––––––––––––––––––––––––––––License or Certificate No.––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––State of Licensure, Date of Licensure ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––Post-Test Answer Form (circle the correct response)1) A B C D2) A B C D3) A B C D4) A B C D5) A B C D6) A B C D7) A B C D8) A B C D E9) A B C D10) A B C DSignature____________________________________________Date Form Sent ________________________________________OCTOBER 2002 DIALYSIS & TRANSPLANTATION 689

WATER DISTRIBUTION DESIGN690 DIALYSIS & TRANSPLANTATION OCTOBER 2002