Going with the flow: the basics of water treatment

The equipment in your water treatment room is among the most important in your dialysis unit. Why? Because that system provides one stream of purified water that is used by each and every one of your patients. If anything goes wrong, they are all at risk for an adverse outcome.

Providing safe water starts with the process of designing and specifying components that go into a treatment system. Safety continues with consistent monitoring and making changes when your monitoring shows that something needs to be addressed.

A lot of thought and experience should go into the water system before it is purchased and installed. One important consideration is how to make sure the components are correctly sized for the needs of your clinic. You cannot just guess at how much water your system will consume, or simply order the same size reverse osmosis (RO) machine that was used in an old unit. Trying to get by with less water than necessary will cause major problems later on down the road.

Below are some of the important planning steps that should go into the design of the water system in your facility.

Work backwards: start building the system from the back end and move forward. Calculate the amount of pure water that will be needed by adding up the amount of water each piece of equipment uses when running at maximum capacity. Consideration should be given to all dialysis machines, reuse machines, and concentrate mixers (both bicarb and acid, if used).

Once the amount of pure water is determined, a reverse osmosis machine should be selected that would provide approximately 30% to 50% more water than necessary so that you have the capacity to handle an extra load or the inevitable degradation of the RO’s product output. ROs are generally rated as having between 50% and 75% “recovery,” which means that it will consume 25% to 50% more tap water than it produces for use in the facility. That means that an RO that produces 10 gallons per minute of product water will send an additional 2.5 to five gallons to the drain as wastewater. The size of the pre-treatment components should be calculated based on the total amount of water your RO will consume, both product and waste.

The carbon tanks are sized so that you have an empty bed contact time (EBCT) of at least five minutes for the primary (worker) tank and five minutes for the secondary (polisher) tank. You must have two carbon tanks: one to remove the chlorine and another to prevent exposure to your patients if chlorine breaks through the first tank.

The water softener should be sized based on the amount of hardness in your feed water. Hardness is usually measured in grains per gallon of calcium carbonate. The harder your water, the larger your water softener needs to be, and the more often it needs to be regenerated.

The water distribution loop should be sized so that you can achieve the desired flow rate for your water requirements without losing pressure. It also needs to be sized so that your pipes maintain a flow velocity of at least three feet per second, to minimize the potential for bacterial growth.

It is essential that the water system be monitored for changes and that action is taken when it is needed to keep your patients safe. It is not enough to simply record the readings of your gauges and flow meters without thinking about what the readings mean. You must be attentive to changes and plan your response in the event that something does change. Don’t assume that your patients will always be safe because your facility designed and installed a good water system. Your water system will change over time—and your feed water can change in an instant!

Monitoring your water system

Monitoring operating parameters (Pressures and flow rates throughout the system)

Establish baseline readings for all of the gauges and flow meters. If you do this when the system is new, you will know when something changes. If you didn’t do this when your system was new, do it now, and do it whenever you update a part of the system.

Establish which changes in the readings will require action on your part. For example, when you get a pressure drop of 10 PSI across a filter, you will know that it is time to change it or back-flush it.

Monitor trends in the reading. Small changes are hard to notice from day to day, but it is easy to see these changes over time because you can see the bigger picture.

There should be a pressure gauge between each component in the water treatment system.

Monitoring quality parameters

Know the quality of your incoming water by taking a direct sample from your building. Do not rely on a water analysis based on a sample from the municipality; this can result in inadequate system design.

Regularly send water samples to your laboratory for chemical analysis. The Association for the Advancement of Medical Instrumentation (see sidebar) requires that you do this annually, but many places experience seasonal changes in the source water. To be safe, test both your incoming and product water quarterly. Make sure that your product water meets AAMI standards at all times.

Monitor the chemical purity of your water by using an indirect measure such as conductivity, TDS and / or percent rejection. Make sure that you set your alarm tightly enough to get a warning before the level of contaminants exceeds the maximum allowable level. (See the AAMI table of standards, included with this article.)

Check your chlorine prior to every patient shift. If you do not have defined shifts, test the chlorine level every four hours. Chlorine should be tested after the “worker” carbon tank and before the “polisher” carbon tank. The water must meet the AAMI standard of less than 0.1 ppm of total chlorine. Remember, it is important to test your chlorines after your system has been running for at least 15 minutes. If you test for chlorine when you first start up the system, you may be testing water that has been in the carbon tank for several hours, and you won’t know if it can remove the chlorine during normal operation.

Test your water for hardness daily, right after the water softener. This test must be done at the end of the day. If you test in the morning, you will almost always get acceptable results because the softener regenerated overnight. If you test your hardness at the end of the day, and the results are high it is an indication that you do not have enough softener capacity to remove all of the calcium. Hardness post softener should be less than 10 ppm.

Test your water system monthly for microbiological contamination. You should draw water samples at a few points in your system: where the water leaves the RO, where it leaves the holding tank (if present) and at the end of your water distribution loop, and where it enters your reuse equipment and concentrate mixing systems. The water needs to be tested for both bacteria and endotoxin.

The AAMI recommendations* state that bacteria must be cultured by an appropriate method and not exceed 100 cfu/ml, with an action level of 50 cfu/ml. Endotoxin must be tested, most often by an limulus amebocyte lysate test, and not exceed 0.25 EU/ml, with an action level of 0.125 EU/ml. If your results exceed the action levels, you must take action to reduce the microbiological exposure to your patients.

* Medicare requirements are based on an earlier version of the AAMI guidelines, and are a bit higher.

This article provides just a small amount of the information you need in order to completely understand your water treatment system. More information is available from a variety of sources, including AAMI, NANT and ANNA (see the Resources section). You can also find a manual titled Monitoring Your Dialysis Water Treatment System that is available as a free download from the Northwest Renal Network (www.nwrenalnetwork.org/watermanual.pdf). -by Jim Curtis, CHT