We have a dual tank (one for mixing and the other for distribution) bicarb system. It is rinsed daily with RO water and bleached weekly, as is done in most places I have worked. Monthly microbiology sampling includes, the mix tank, distribution tank and the loop return. All 3 samples are collected at the end of the day post system rinsing. The loop is left overnight with static RO water in it. It is a MarCor bicarb system [no head tanks]. My question to all of you out there is does anyone with a similar set up sample in the morning instead? Currently we use just one of these 2 options: Sample at night (which is too late for FedEx) and refrigerate and ship the next afternoon - or - sample in the morning before mixing bicarb (RO water in the loop over night) and ship the sample the same day it was collected. I am trying to find a way to sample fresh RO water from all 3 sample sites that can ship the same day they are collected.
Just like your water system, your samples have to be drawn "worst case" which would mean right before your bleach disinfection. This could be problematic depending on what day of the week you do your bleaching. We have done our own "study" and saw that we can refrigerate samples overnight and ship the next day with having little to no effect on the results.
Chuck Weddle, CHWS Certified Hemodialysis Water Specialist Technical Manager Independent Dialysis Foundation, Inc.
DISCLAIMER: The views I express are mine and may not be the same as my employer.
we have the same system. we run the loop with 10 gallons ro water with the distribution pump running every night after rinsing so that the water is not static. We sample in the am before the water is dumped from the dist. tank.
Chuck is right about the worst case scenario, but AAMI does give you some wiggle room because the worst case could be Saturday evening, which obviously is not practical. When we used the DaVita lab, we had to start drawing cultures in the morning to have everything boxed up in time for FedEx. The DaVita lab would reject cultures that had been drawn too far in advance. The lab didn't take deliveries on Sunday, etc.
If your water treatment system has been validated, are you drawing more cultures than you need to? I am working off memory here, but I think the standards state that you need to sample where the treated water enters, in this case, the bicarb tank. Some people might argue that your machine cultures are sampling the bicarb loop. Could the samples you are drawing be part of troubleshooting a problem and not routine surveillance?
I think the best day to draw cultures is the Friday before a disinfect Sunday. That is the worst case scenario where you can still get your cultures to the lab. If you have a bad culture, you have already disinfected the water treatment system.