Water Bath- Definition, Principle, Parts, Types, Procedure, Uses

A water bath is a piece of scientific equipment used to maintain a steady temperature for a prolonged time when incubating samples.

A water bath is preferred over an open flame when heating flammable substances. It is employed to enable some chemical reactions at high temperatures.

A big container filled with warm water makes up a hot water bath. It has different design combinations, sizes, and proportions. A laboratory water bath’s container capacity ranges from 12 to 32 liters for a standard model and 50 to 100 liters for a large water bath. Most water baths feature a digital or analog interface that users may use to set the desired temperature. In contrast, some water baths include a reader that uses a current to regulate the temperature. A shaker is another feature of the water bath that is useful for homogenizing the test solution

Water Bath
Water Bath

Its mostly utilized in clinical and microbiology labs, university labs, environmental research, and even food technology for warming reagents, sample thawing, corrosion tests, and bacteriological investigations, among other applications. A water bath is a tool that needs additional supporting instruments to function. An incubator, a micropipette, a centrifuge, and a laboratory oven are typically used in tests involving a water bath.

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Principle of Water Bath

The sensor converts the temperature of the water into a resistance value, which is then amplified and compared by an integrated amplifier. This produces the control signal, which effectively regulates the average heating power of the electric heating tube and keeps the water at a constant temperature.

Parts of Water Bath

  • Container 

A laboratory water bath’s container comprises an insulated metal, like stainless steel. Test samples are maintained in hot water for a lengthy time in a container.

  • Container lid

It is mainly constructed of insulated metal or heat-resistant glass. The lid keeps the container covered, preventing water evaporation.

  • Heater

Temperature sensors are used as a heater in a laboratory water bath to help create heat.

  • Thermometer

It helps gauge the water bath’s temperature. It may be integrated or added on its own. 

  • Thermostat or regulator

It aids in maintaining a steady temperature in a water bath.

  • Propeller or stirrer device

It is found in circulating water baths which promotes water circulation inside it.

  • Outlet

It aids in removing the water from the container.

  • Indicator light

It should be present in every water bath. The water bath is warming up while the light is on. The light will be turned off to maintain the desired temperature if the water bath achieves it.

Types of Water Bath

Shaking Water Bath

The water bath’s shaking characteristic is more precisely controlled for liquid flow. An on/off switch controls the shaking. In microbiological techniques, regular shaking allows liquid-grown cell cultures to mix continuously with the air. The features of the shaking water bath include high-precision temperature control, easy temperature adjustment, a precise and clear indication, and outstanding and dependable performance. For easier experimental observation, lighting equipment is provided in the workshop. The cabinet has a fan, and a forced-air convection unit fitted to disperse heat more evenly.

Some of the main benefits of this type of water bath include the user-friendly keypad operation, the straightforward bath drains, the programmable shaking frequencies, etc.

Circulating Water Bath

It is also known as a stirrer water bath. In the baths with circulating water, the water is properly circulating. Stirrers or circulating water baths may be useful for applications where the samples must have consistent or uniform temperatures. The circulating water bath uses continuously circulating water to efficiently and dependably obtain and maintain the desired water temperatures required for the cooling or heating of samples and reagents. It enables quick heating or cooling of samples across a wide temperature range. Enzymatic and serologic testing may be used for these purposes. It receives proper circulation, which leads to a more stable temperature.

Non-circulating Water Bath

Such laboratory water baths rely on the convection mechanism rather than heating the water uniformly. As a result, the water bath’s capacity to control temperature is less exact. We can also add accessories to stir the water bath to enhance heat transmission. Water baths are safe to use up to 99.9 °C. When the temperature is greater than 100 °C, substitutes may be used.

Polycarbonate Water Bath

Inside the bath, there is a controlled heating system. The container is made of transparent polycarbonate, and its temperature can reach 100 degrees Fahrenheit.

Analog and Digital water bath

Analog water bath

The most basic kind of water bath is an analog one. It is affordable and simple to use. However, it only has a few issues. The analog water bath’s accuracy is lower than the digital water bath’s, which is the first issue. There isn’t a display board in addition to that. The water’s true temperature won’t be visible as a result.

Working mechanism of analog water bath

When the machine is given a power supply, the main indicator will glow. Then the current will go to the thermostat. From the thermostat, the current will flow through the water immersion heater. The thermostat will permit current to pass through the heating rod if the water’s temperature is lower than the predetermined level. Consequently, the water will start to warm up. The thermostat will shut off when the water temperature reaches the predetermined level. The heating rod won’t, therefore, receive any current. The water’s temperature then starts to drop. The heating indicator will also stop glowing.

Digital water bath

An upgraded version of an analog water bath is a digital water bath. It’s extremely pricey. However, using it is simple. This version is more accurate. Similar to that, it has a display board that enables the user to view the real temperature of the bath’s water.

Working Mechanism of digital water bath

The solid-state relay (SSR) and PID controller work together to manage the water immersion heater. The controller will deliver a certain DC voltage to the relay if the water temperature is below the predetermined value. The relay will turn on, causing the AC to flow to the heating rod. As a result, the heater starts to warm the water. The PID controller will constantly activate and deactivate the relay when the actual temperature of the water approaches the desired value. Thus, the heating rod will continuously cycle ON and OFF.  As a result, the water bath contributes to the maintenance of a nearly precise result with a variance of no more than 1°C. The sensor measures the water’s temperature using a resistance temperature detector (RTD). The temperature is then converted to a resistance value, which is supplied to the controller. This incoming signal will be compared to the preset value by the controller.

Controls of a Laboratory Water Bath

Temperature controller: A temperature controller, either digital or dial, is a standard feature of all water baths.

Safety controller: A safety controller is often found above the temperature controller or connected to the indicator light in most water baths. A safety controller aids in determining the highest temperature that the water bath should reach. The safety light will turn on if the water bath somehow manages to meet the temperature that the safety controller has established. Even with a higher temperature, a water bath cannot achieve a temperature greater than the safety settings.

Shaking controller: It may enable us to accelerate, decelerate, or activate the shaker.

Operating procedure of Water Bath

  1. Ensure the equipment is clean and the temperature indicator is calibrated by the due date.
  2. Plug in the power source.
  3. Make sure the water in the bath has enough depth for the heating element to be poured in.
  4. Turn “ON” the instrument’s main power source.
  5. In order to set the desired temperature, press the SET key. The temperature can be changed by pressing any or both of these buttons.
  6. Use a calibrated thermometer to confirm the temperature.
  7. The temperature sensor will retain the set temperature whenever a water bath is used.
  8. After use, turn “OFF” the main power source and the instrument’s mains.
  9. After usage, completely dry the instrument and then replace the lid.


  • It can be used for reagent warming, substrate melting, or cell culture incubation.
  • The water bath is the preferred heat source for heating flammable compounds because it allows some chemical processes to occur at high temperatures.
  • It improves the solubility of poorly soluble compounds.


  • The alcohol lamp’s flame may reach temperatures of up to several hundred degrees Celsius. The melting process of the material cannot be documented or viewed if it is heated directly by the alcohol lamp fire in the experiment. The sample can be heated evenly in the lab water bath, avoiding direct heating’s excessive intensity and uncontrollable temperature swings.
  • Water baths offer a larger surface area, allowing your samples to be heated more quickly.
  • Even if you are simultaneously heating several samples, there is very little chance of temperature variations because water baths can hold a significant amount of heat.


  • Like an untreated hot tub, warm water exposed to the environment can hold and support undesirable microbial activity.
  • If tap water is used in the water bath, it must be replaced frequently; distilled water does not require frequent replacement.
  • It is solely reliant on power and is not suitable for the usage of heat-sensitive samples.


  • Make sure the bath is seemingly electrically safe before its use. For instance, a current safety check could be performed for obvious issues with the main connector and lead, external switches, or controls.
  • Before turning on/operating controls and plugging into a mains power outlet, make sure your hands are dry.
  • Avoid touching the shaker mechanism or circulation impeller with your hands, hair, or loose clothing. If possible and appropriate, cover your device when operating at temperatures exceeding “hand hot” (>50°C).
  • Make that the water level is kept at the proper level, especially when operating at higher temperatures, such as those close to 95°C. Water levels should be routinely checked, and only distilled water should be used to fill them. This is necessary to stop salts from building up on the heater. Do not rely on the thermal cut-out functioning well when the heating elements are not covered by water; this will prevent overheating and potential electrical damage.
  • Use an appropriate algicide, fungicide, or bactericide if the bath will be used constantly for a long time, such as >24 hours, to prevent the growth of undesired and potentially pathogenic organisms in the bath water. To reduce hazards from corrosion, leaks, and electrical failures, this must be compatible with the tank’s materials and other parts.
  • Ensure to thoroughly clean the bath after usage, especially if it was used to incubate potentially pathogenic sources and poisonous or caustic items that could end up in the bath water. If powerful detergents or disinfectants are to be used, wear rubber gloves and perhaps eye protection.

Examples of Water Bath

Laboratory water bath WTB11 (Manufacturer: Memmert GmbH + Co. KG)

  • It is considered ideal for heated storage and calibration in the industrial sector and the temperature management of ointments, emulsions, samples, plates, and nutrient solutions in laboratories.
  • It features a two-stage safety system to prevent overtemperature with an individually adjustable overtemperature alarm.

Circulating water bath HBR 4 control (Manufacturer: IKA)

  • It is cylindrically shaped with heating elements integrated into the bath base.
  • Low-viscous oil or water are two possible heat transfer mediums.
  • Target temperature, actual temperature, safety temperature, and speed are digitally displayed.

Shaking water bath SWB-110X series (Manufacturer: Biobase)

  • It features a visual and audible alarm and turn-off recovery function.
  • It has stainless steel lid, which reduces evaporation and heat loss.
  • It is designed with double over-temperature protection and an anti-drying feature.

Circulating water bath MDBS series (Manufacturer: Medline Scientific)

  • The Medline MDBS-14, 14 Litre Water Bath, made of polycarbonate and has a safety thermostat, offers ideal temperature control for samples.

Shaking water bath WB-S30 (Manufacturer: Bioevopeak)

  • A large background LCDs the measured value, set value, setting time, and remaining time.
  • High-precision temperature control facilitates the operation’s resume if the power cuts out suddenly.
  • High-precision speed control is achieved using PID feedback and accurate and consistent motor speed.
  • Design features include a slow start, automatic locking when the speed gets out of control, and a customizable start speed to stop liquid from shaking the bottle from splashing.


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About Author

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Prakriti Karki

Prakriti Karki completed her B.Sc. in the field of Microbiology. She is interested in working in the interface of immunology, microbiology, synthetic biology, bioinformatics, and open science. She has worked as a project lead at Media Lab Nepal, as a research associate in the BMSIS program, and as an awareness community member at the iGEM WiSTEM initiative.

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