Choosing the right water system for a lab glassware washer
You are ready to buy a new glass washer for your lab, but you are unsure what water feed system to use? You probably already know what grade water you want to feed your glass washer. In most cases, except for special circumstances for very sensitive applications an ASTM Type II reagent grade water source will be sufficient for your lab glassware washer. ASTM Type II is defined as water that has greater than 1 MΩ/cm2 resistivity. Lower grades are not recommended for most application and Type I water rinses (>18 MΩ/cm2 might be necessary for especially sensitive application like HPLC and mass spectrometry. While there are several different ways for water purification like filtration, different kind of filtration, sterilization by UV radiation, adsorption by activated charcoal, to achieve the resistivity required for lab-grade water, the water need either to be distilled or deionized. Distillation requires the heating of water to the boiling point and collection of the condensate form the vapor. This method is the oldest method to produce lab-grade water, but it consumes large amounts of energy, and is unable to remove contaminants that have a lower boiling point than water. The most commonly used method today is deionization. This process uses two ion exchange resins over which the water flows. One resin exchanges cationic contaminants for an H+ and the other exchanges anionic contaminants for a OHion. Both resins can be mixed together in one container. The quality of the water depends on the lengths of the exchange column and the quality of the resin. The resin has to be replaced from time to time. It can be regenerated, and many water purification companies sell resin cartridges with regenerated resin, but new (virgin) resin has a higher cleaning capacity, and does not carry the risk of cross-contamination from other applications.
One main feature you need to be aware of when choosing a lab water purification system for your lab glassware washer is the water use of the washer. If you do not require a large cleaning capacity and you are looking for washer with a small footprint like e.g. the 24” Miele G789, the Labconco undercounter FlaskScrubbers, the Lancer LX, or the untercounter washers from Hotpack, a low flow water system might be the right solution for you. Low flow glass washers with DI-water requirements for up to 6 liters/min can use low-flow water systems that might be a much more affordable alternative to a high-throughput-system. Most glass washer, however, require a larger water flow, and high flow system with flow capacities of 15-40 l/min will be able to fill the need. Some lab water purification system comes with pressurized storage tanks and spare DI-filter cartridges.
Another feature that should be considered when choosing a water purification system is the ease of the maintenance. Filter cartridges need to be exchanged from time to time, and some systems require a maintenance plan from the manufacturer. Other systems can be serviced easily and within a few minutes by the user.
Quick reference guide for choosing a water purification system for a lab glassware washer: The following questions should be answered before choosing a water purification system.
What water quality do I need? Water quality needs are based on the applications for which the glassware will be used. Most application will require ASTM Type II water with a resistivity of >1 MΩ/cm2
What water flow capacity is needed? Some small glassware washers have a low flow requirement and might be able to be fed by a low flow water purification system that can be more affordable alternative.
How much maintenance am I willing to do myself? Service contract for routine maintenance and cartridge exchanges can offer peace of mind, but doing cartridge exchanges yourself might be more cost efficient alternative that has potentially the additional advantage of reducing downtime of the system.
Is a point-of service DI-water source needed additionally to the glass washer feed? Is the water purification only meant to provide a source of the DI-water feed for the glassware washer, or is the possibility to obtain water for other applications also required? Some water purification systems will include a point-of service access to the DI-water. Frequently asked questions
What is ASTM Type I and Type II water? The American Society for Testing and Material (ASTM) sets standard for the amount of ionic contamination in lab-grade water. ASTM type I water has the highest purity and a resistivity of >18 MΩ/cm2, which corresponds to an ionic contamination of less than 1ppb. ASTM Type II water has a resistivity of >1 MΩ/cm2 or less than 500ppb total ionic contaminants.
Do I need a rinse with ASTM Type I water? ASTM Type II water is sufficiently pure for rinsing of laboratory glassware for most common applications. However there are certain applications that are more sensitive to ionic contaminants like e.g. most analytical chemistry, molecular biology and tissue culture applications. In these cases it might e necessary to feed ASTM Type I water to the glassware washer for rinsing.
Do I need a service contract for my DI-water system? All deionizing water purification systems require regular maintenance as the ion exchange resins have a limited capacity and need to be exchanged on a regular basis. This need to be done by trained technicians for many systems. However, there are some systems that allow exchange of the filter cartridges by the user within minutes. This might reduce down-time and costs for maintenance contracts.
Will I have access to the DI-water aside from the feed to my glassware washer? Some water purification systems provide feed water for the rinse cycles of laboratory glassware washers alone. However, there are system available that will have a point of service (POS) access to DI-water.
Is ASTM Type II-water nuclease-free? Working with nucleic acids in particular RNA can be challenging due to the ubiquitous nature of RNAse-contaminants. ASTM-type II water is not rated for its content of organic matter including nucleases. If nuclease-free rinse water is necessary for your applications the water purification system should include appropriate ultrafiltration and, if very low organic contaminant concentrations are necessary, UV-oxidizer-steps.