As discussed earlier, no matter what type of work is done in a laboratory, it’s almost certain that lab water is required to carry out certain processes. Due to the sensitive nature of laboratory work and the need for as many factors to be controlled as much as possible for effective, accurate testing and research, laboratory water must be pure, with defined levels of acceptable impurity.
There are four levels of water purity recognized in the water purification industry, each of which are used for specific applications in the laboratories and must go through various processes and technologies to achieve a certain standard of purity.
Types of Laboratory Water
1. Feed (Raw) Water
Feed water is also referred to as raw or potable water, and the quality of it is dependent on its source. Whilst deep water is naturally filtered by layers of rock and soil, water from surface sources like lakes and reservoirs is at risk of environmental contamination.
Raw or feed water is typically identified by measuring its colour, odour and turbidity. You can also look for chemical characteristics like pH and hardness, as well as bacteriological characteristics. Some of the most significant contaminants of feed water include dissolved ions, minerals, microorganisms and organic compounds.
Feed water should always be tested, and have appropriate pre-treatment measures conducted, to ensure that the quality is sufficient enough not to damage the downstream purification technology.
Pre-treatment filters
The most common type of pre-treatment are media filters most often comprising of sand and carbon filters. Depending on the water source and the nature of contaminants, catalytic media can be used for water pre-treatment.
Another step commonly taken is the installation of a water softener, reducing the hardness level of water before it reaches the RO membrane; hard water causes scaling of the RO membrane and reduces its lifespan.
1. Type 3: Primary Grade Water
Primary grade water (Type 3) uses the pre-treatment filters and RO technology, the most cost-effective way to reduce water contaminants.
Removing up to 99% of feed water contaminants, RO sees water flow from a less concentrated solution through a semipermeable membrane to a more concentrated solution. By applying external pressure to the more concentrated side, the osmotic flow is reversed, which forces the water through the membrane, and deposits the impurities on the surface.
RO water is most commonly used at the starting point for many applications in laboratories, including feeding glassware washing machines and autoclaves. It is also used as a pre-treatment for ultrapure water systems, or anything that’s considered non-critical.
2. Type 2: General Laboratory Grade Water
Also known as general laboratory grade water, Type 2 water is produced through a combination of reverse osmosis, and an additional technology such as ion exchange or electrical ion exchange (EDI).
Deionisation, or ion exchange, removes ions from RO water by using synthetic resins. Chemical reactions occur as the water passes through the ion exchange beads, resulting in the removal of ions. This process is continued until all unwanted ions are replaced by hydrogen and hydroxyl ions, which form pure water once combined.
EDI is an active purification technology that combines electrodialysis with ion exchange. Water is passed between an anion permeable membrane and a cation permeable membrane within an EDI cell. The cell chamber contains loosely packed ion exchange resin. Ions are then attracted to the oppositely charged electrode, but they’re flushed away before they’re able to reach it, which means they’re removed from the water.
Together, these two processes create Type 2 water, which has a resistivity of 1-15MΩ-cm, making it suitable for general applications such as buffer and media production, general chemistry and spectrophotometry, analysis of calcium build-up in water and also used in preparation of type I water.
3. Type 1: Ultrapure Water
With a resistivity of 18.2 MΩ-cm at 25°C, ultrapure (Type 1) water is a requirement for analytical laboratories. Flow cytometry, pyrogen sensitive applications, and cell and tissue culture are all typical applications for Type 1 water.
Water with this type of resistivity can still contain organic contaminants, endotoxins and nucleases which don’t impact on resistivity values, so other technologies are required to eliminate them.
Equipment that produces Type 1 water is often referred to as a “polisher”, and can be fed from a localized reverse osmosis system, or a centralized ring main.
Bacteria and organic levels are maintained lowly, through a dual wavelength ultraviolet (UV) light (185nm and 254nm). The water flows through a vessel containing a UV light, and as it passes through, the light damages any genetic molecules that are needed for reproductive functions. This damage prevents the microorganism from multiplying or replicating, which means no infection can occur.
An ultrafilter (UF) can also be used to produce DNase/RNase free water. By using size exclusion, ultrafiltration removes particles and macromolecules, and is sometimes charged to attract contaminants. This technology is employed at the end of the system, to ensure the near-total removal of macromolecular impurities.
Using the right equipment, you can purify water in your laboratory for various analytical needs