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Water Bath Protocol


A water bath is a piece of laboratory equipment that helps bring your materials to a particular temperature, catalyze chemical reactions such as restriction digests needed in molecular biology, and thaw cell lines. There are many different types of water baths that exist as scientists work with tubes and bottles of different sizes in the lab. Some water baths contain individual slots for heating up tubes while other water baths hold many liters of water to incubate bottles and containers. Water baths can also be placed in walk-in refrigerators to achieve a temperature between 4°C and room temperature. This general protocol suits almost any water bath.


Watch the video for tips on using a water bath in the lab.


  • Water Bath
  • 10% bleach or 70% ethanol
  • Distilled water
  • Disinfectant
  • Thermometer
  • Water bath weights and floats


    None needed


  1. Ensure that the water bath and water bath cover are cleaned before filling the water bath with water. You may use a 10% bleach solution or a 70% ethanol solution to wipe down the inside of the water bath.
  2. *Pro-Tip* To properly maintain the water bath, empty and clean it regularly.

  3. Determine the amount of water needed to fill the water bath, and be sure to know what the maximum fill capacity is. Look for a “fill” line inside the water bath or read the user manual. If you’re filling up a water bath with individual slots for tubes, remember that when you add the tube to the slots, it can cause the water level to rise up and flow over the edge of the slide.
  4. Fill the water bath with distilled water, not tap water, to prevent salts from accumulating on the surfaces of the water bath as the water evaporates from the tub. Disinfectant may be added to prevent growth of bacteria or fungi. There are disinfectants designed to be used in water baths with instructions on the bottle, for example, number of drops per liter.
  5. Place a thermometer in the water bath. Oftentimes, the water bath will have a spot to secure the thermometer in place.
  6. Turn the water bath on and set the appropriate temperature as described in your protocol. How to set the temperature will vary depending on the model of water bath, but will likely involve a dial or a digital display you can set to the correct temperature. Set up your water bath so that it will reach the desired temperature by the time you need it for your experiment. Water baths tend to heat up relatively slowly. Place the water bath cover on the top of the water bath to prevent evaporation and maintain the desired temperature. This also helps the water bath heat up quicker.
  7. *Pro-Tip* Set up the water bath 30 minutes to 1 hour before you need to use it to allow the temperature to stabilize.

  8. Use water resistant markers, such as permanent markers, to label your tubes and/or containers that will go into the water bath. If you’ll need to sterilize your items after removing them from the water bath, be sure to use a marker that is also resistant to chemicals such as ethanol. Writing on the tops of the tubes and lids of items to be placed in the water bath is often better than writing on the side of the tube. This way, as items are floating, you do not need to necessarily maneuver the bottles or tubes to identify them.
  9. Once the water bath is at the correct temperature, remove the lid and place your tubes or bottles into the water bath. Many items may float in the water bath when they are placed inside. Water bath floats can be used to secure tubes in place and water bath weights can hold bottles in place.
  10. After putting your tubes or bottles in the water bath, place the lid back on. Note the time that you’ve put your materials in the water bath so that you know when to take them out after your incubation is over.

Note: If you regularly use a water bath in the lab, you can leave the water in it from previous uses. However, you will still need to regularly clean out the water bath even if you are using disinfectants as described above in step 3. You will also need to maintain the appropriate water level in the water bath so before use, make sure that there is enough water inside.