Expert Insight: How to optimize water purity at a reduced cost

Watch this expert on-demand webinar to learn how to maximize the efficiency of water preparation in your lab

04 Jun 2020

Brandon Van Leer


Impurities found in all drinking water can have a negative influence on your scientific analyses. In this on-demand webinar, expert Nadia Brandes, from Sartorius, explains the sources of water impurities and how to optimize water purity to the standard needed for specific applications. Brandes also demonstrates how to save resources by providing a theoretical and practical understanding of how to work most efficiently with your lab water system.

Read on for highlights from the live Q&A session or register to watch the webinar at any time that suits you.


Q: How can RNase/DNase-free water be prepared in the lab?

NB: I would definitely recommend using an ultrafiltration module. We have two options for this. You can have an integrated ultrafiltration module, which is inside the system. The big advantage of this is that it's also set up inside the loop. This means that typically ultrapure water systems are recirculating for 15 minutes once an hour. The whole water is pushed through the water purification cycle, through all titration components. As a result, the water is really cleaned up.

The other option is to use an open ultrafilter at the outlet of the system, so it's directly connected at the dispense outlet. If you use such a kind of ultrafilter in the dispense outlet, you must take care that before collecting the water you dispense approximately 900 milliliters first, to make sure you have no rest water standing inside the filter and that you get the purified water out of the filter housing. 

Q: How much water is required to obtain 1 liter of purified water using reverse osmosis?

NB: In a reverse osmosis system, you typically have concentrates and the product waterline. You must get rid of the high salt-concentrated water in order to purify the water. We can have different kinds of setups. Some systems use 60% product water and 40% wastewater, or 60% wastewater and 40% product water. You can adjust this with different kinds of components. Roughly, you could always go in with 100% and come out with 50% product water and 50% concentrate water. So, for 1 liter, you would need 2 liters.

Q: What is the best method to remove endotoxins in cell culture applications?

NB: Here, we definitely need to keep in mind that we need to differentiate between mammalian cell culture and bacterial cell culture. Endotoxins typically only affect mammalian cell cultures. It is important, like for RNA, for the DNA removal to implement an ultrafiltration module to the system. It can be installed inside the system or, like for RNA, for the DNA removal, attached to the dispense outlet of the system.

Q: What is the best purification step for TOC critical applications?

NB: The bag typically is used as a standard polyethylene tank. They have a standard lifetime like PE tank. From time to time, you have to clean a PE tank, but in our case, it's easier. We have a big advantage with our system that the Bagtank is just disposable and can be removed, and you do not have to clean it. The storage of the water is independent of the material type. It doesn't matter if it is a polyethylene tank or it is a bagtank. Both storage opportunities are quite efficient and fulfilling in their effect. Finally, what you must keep in mind is that you are storing reverse osmosis water or Type 2 water. This is different from trying to store Type 1 water. There are still some residues inside the water. It's not as clean as Type 1 water but, therefore, it's also not so affected by the atmosphere. So, the quality of the water stays quite constant inside the bag or a storage PE tank over a long period of time. A good recommendation is to not oversize the tank system. You should ensure that the bag or the tank is cleaned at regular intervals. Typically, we size systems so that you can refresh the water in the tank at least once a day.

Q: How often do we have to change consumables on the purification systems?

NB: This depends on the system itself. Reverse osmosis modules typically have the longest lifetime. Reverse osmosis modules should be changed every 12 to 24 months normally. This depends a little bit on your incoming water - if you have very dirty incoming water, then you may have to change it more often. For consumables of an ultrapure Type 1 water system, we typically say that you should at least change the ion exchange cartridge, which produces the 18.2 MΩ quality water, at least once a year just to make sure that your product water quality remains high.

Q: How many days do you need to clean the tank?

NB: The tank is typically cleaned every six months, at similar intervals in both PE tanks and bagtanks, which are recommended to be cleaned every six months. In our case, it takes approximately five minutes to clean because you have this disposable material. For other storage tanks, for example PE tanks, you typically have longer sanitization times. If you are working with a drug, which needs to go into solution first, then you need to leave the cleaning solution inside the tank. Afterwards, you have to flush the tank again to make sure that you get rid of all those chemical residues inside the tank. In this case, if you use a PE tank, it takes much longer than a bag for the sanitization procedure. 

Q: What is the cleaning procedure for the Type 2 water storage tank?

NB: Normally chlorine is used for PE tank cleaning. In our case, we do not clean the tanks at all. We just place in a new one because they’re disposable. You also have the advantage that you will never have, for example, chemical residues after sanitization or cleaning a tank because you just throw the old one away and place in a new one. For PE tanks, you still use chlorine for sanitization of the tank.

Q: If I am working with oil for oxidation studies with double-distilled water, will this influence my experimental results?

NB: The water quality of double-distilled water and produced ultrapure Type 1 water is more or less the same. I think if you use double-distilled water then your main issue is that there may be organic residues inside your water. You can modularize, in principle, your ultrapure water systems. This means that you have different options available to the application of what you're running. If you need organic-free water, for example, then you have the option to run pretreatment systems with reverse osmosis in front, followed by using an ultrapure water system typically in combination with a UV lamp to reduce the organic content inside or volatile organic components. You can nearly modularize an ultrapure water system to be of the same quality as a double-distilled water system. 

Q: How efficient is the bag type storage and can it be reused?

NB: The bag is disposable - you just exchange it and you do not reuse it. I would say it's more efficient to use the bag system than a PE tank because it's fast and you save a lot of time. If you use a PE tank, you cannot use the system when it’s being cleaned - depending on the size of the tank, it could take three to six hours approximately.

Q: Can you dispense 100 to 150 liters of Type 1 water per day?

NB: Yes, you can. I would recommend making sure that you have a really good pretreatment in front. You need at least to use a Type 2 water system or ion exchange purification step so that the feed water is below 1 microsiemens. Too many ions inside the water would eventually also affect your cartridge capacity in the Type 1 water system. The more purified the feedline water is, the longer life your cartridges will have in the Type 1 water system.

Q: Does it make sense to store Type 1 water in a PE tank over time?

NB: It doesn’t make sense to store Type 1 water at all. To make sure you get the highest water quality it is best to dispense the water directly. The Type 1 water is purified to the maximum technical point that can be achieved - that means there is nearly nothing inside the water anymore. All elements have been removed and, therefore, the Type 1 water reacts quite strongly with the atmosphere. So, as soon as you walk some meters with the water, some ions will get inside. If you do not cover the water, then the quality will immediately drop.

I would always recommend preparing fresh water for use in very critical applications. If you have to store water, then I would always recommend using standard glass bottles. The smaller the stored water volume is, the less likely you are at risk of contamination. The best way is to dispense the water directly to ensure the highest water quality. 

Q: Can water from a Type 1 system be used to trace organic applications?

NB: Yes, absolutely. For trace organic applications, such as HPLC, UHPLC and gas chromatography, the water must be free of organic traces. You can also optimize your Type 1 water by optimizing your pretreatment water conditions. I would always recommend for analytical applications to make sure that you take out as many organic traces as possible by using a reverse osmosis system as a pretreatment system. The reverse osmosis module takes out 95% of all the organic traces inside the water. The rest is polished by activated carbon and the UV lamp inside the ultrapure water system. This is the ideal combination, and this works for both trace analyzers.

For more information on the systems and consumables discussed, visit 

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