A water bath is often shared between multiple users causing grease, salts and other dirt from sample containers to build up quickly. On top of that, its warm and moist environment make it a perfect habitat for various microbes. We'll explain best practices to follow to mitigate these issues.
To ensure a water bath is kept clean and in optimal condition, it should be cleaned regularly. Before you start cleaning the water bath, unplug it, let the water temperature drop, and empty the bath. Clean the bath with soapy water and a cloth. Avoid the use of chlorine-containing cleaning supplies, such as bleach, and abrasive scrubbers, because they will damage the bath and cause it to rust.
Afterwards, thoroughly rinse the bath with water to make sure no soap is left behind. It is important to refill the bath with the right kind of water. Tap water is too impure causing a quick buildup of salts. Extremely pure deionized water such as MilliQ or Barnsted Ultrapure is also not good as it can cause corrosion. Instead, use distilled or reverse-osmosis purified water to refill your bath.
Although regular cleaning is ultimately the only way to keep your bath in good condition, there are some tricks to extend periods in between cleanings. Commercial biocides such as Clear Bath prevent the growth of microbes and help keep your bath clean longer. Make sure to check that the substance is not affecting you sample and that it doesn’t require special treatment upon disposal.
Another option is thermally disinfecting your bath (heating > 60°C for 30 min.) which will destroy most of the algae, fungi, and harmful bacteria. Alternatively, you can add a small piece of copper wire or a copper coin as copper has antibacterial properties. Buildup of salts and dirt can be limited by cleaning of your sample container before putting in the bath.
Another option is to get rid of the water altogether and use a bead bath. Bead baths are specially designed to maximize heat transfer to the beads, but if you don't have a new water bath in your budget, any general purpose water bath can be used with bath beads.
Left: Clear Bath algae inhibitor; right: Lab Armor Bead Bath