Can distilled water grow bacteria?

Distilled water is water that has been boiled and condensed to remove impurities, minerals, and contaminants. This process kills most microorganisms, including bacteria, that may be present in the original water source. However, distilled water is not necessarily sterile and free of all bacteria. Under certain conditions, bacteria can grow in distilled water over time. This article will examine whether and how bacteria can colonize and propagate in distilled water.

What is Distilled Water?

Distillation is a water purification process that uses heat to separate pure water from contaminants. Here are the key steps in making distilled water:

  • The water is boiled, turning it into steam.
  • The steam is cooled and condensed back into liquid water, leaving behind solid impurities.
  • The condensed liquid water is collected, resulting in distilled water.

This heating and condensing process removes salts, minerals, metals, bacteria and viruses from water. Distilled water has a neutral pH of around 7 and low mineral content.

Compared to tap or bottled water, distilled water tastes flat or bland due to the lack of dissolved minerals that give water flavor. It is also aggressive, meaning it tends to dissolve substances it contacts.

Is Distilled Water Sterile?

Strictly speaking, completely sterile water does not exist outside of specialized laboratory settings. However, the distillation process comes close to sterilizing water by removing or destroying the vast majority of bacteria, viruses, protozoa and other microorganisms.

Here’s an overview of how the distillation process eliminates microbes:

  • Boiling – Heating water to the boiling point of 212°F (100°C) kills most vegetative bacteria and viruses.
  • Vaporization – Converting liquid water to steam leaves behind solid contaminants including microbes.
  • Condensation – Recondensing steam into liquid does not introduce new microbes.

However, distillation does not remove 100% of all microorganisms under typical conditions:

  • Endospores – Some bacteria produce dormant endospores that can survive boiling.
  • Protozoa – Parasites like Giardia may persist through distillation.
  • Recontamination – Microbes can be reintroduced during storage and handling.

So while distilled water is one of the purest forms of water available, it is not guaranteed sterile immediately after the distillation process. Additional sterilization steps would be required to achieve true sterility.

Can Bacteria Grow in Distilled Water?

Even though distilled water starts out free of most bacteria, it does not necessarily stay that way. Several factors influence whether microbes can grow in distilled water over time:

Lack of Nutrients

Most bacteria require certain nutrients to grow, such as carbon, nitrogen, phosphorus, sulfur and trace metals. Since distilled water is devoid of these nutrients, it provides a harsh environment for bacterial growth.

However, some bacteria are oligotrophic, meaning they can survive and replicate in nutrient-poor conditions. Examples include Pelagibacter ubique, a member of the SAR11 clade of marine bacteria known for its tiny genome and metabolic flexibility.

Reintroduction of Microbes

Distilled water fresh from the still is hot and bacteria-free. However, as soon as it comes into contact with air, containers, tubing or other surfaces, microbes can be reintroduced.

For example, environmental bacteria may settle from air. The natural microbial flora of skin can contaminate distilled water during handling. Once bacteria gain access, they can proliferate if conditions become more favorable. Proper sanitation and sterile techniques help minimize contamination.

Biofilm Formation

While suspended freely in distilled water, individual bacteria struggle to overcome the lack of nutrients. However, bacteria can adapt by adhering to surfaces and forming matrix-enclosed biofilms.

Within biofilms, microbes generate their own nutrients and create microenvironments suitable for growth. Diverse bacteria can inhabit biofilms, including Legionella, Pseudomonas, Acinetobacter, and Klebsiella species.

Biofilm formation poses a contamination risk within small cracks, joints, and dead-ends in storage tanks, tubing, and water handling equipment exposed to distilled water. Maintaining system integrity and performing periodic disinfection helps control biofilm growth.

Changes in Water Chemistry

The longer distilled water is stored, the greater the chance that its chemistry changes in ways that facilitate microbial growth:

  • Absorption of atmospheric gases like carbon dioxide can alter pH.
  • Leaching of minerals from piping can increase nutrient levels.
  • Temperature changes may support mesophilic bacteria.

Nutrient spikes allow bacteria to rapidly exploit these transient opportunities. Routine testing and water quality maintenance reduces chemical changes.

Types of Bacteria in Distilled Water

Many bacterial taxa have been detected in distilled water samples, including:

  • Acinetobacter – Aerobic non-fermenters, some multidrug resistant
  • Bacillus – Endospore-forming rods, include B. cereus and B. megaterium
  • Burkholderia – Opportunistic pathogens adapting to diverse environments
  • Corynebacterium – Clubbed rods, common skin flora
  • Legionella – Cause of Legionnaire’s disease from warm water systems
  • Micrococcus – Ubiquitous, aerobic, form tetrads
  • Pseudomonas – Aerobic rods, efficient metabolizers, biofilm formers
  • Sphingomonas – Chemoheterotrophs using a variety of organic compounds
  • Stenotrophomonas – Emerging multidrug resistant opportunistic pathogens

Both gram negative and gram positive species are represented. While many bacteria in distilled water may not cause illness in healthy people, opportunistic pathogens present a risk to vulnerable populations.

Factors that Allow Bacterial Growth

Several key factors influence the ability of bacteria to propagate in distilled water:

Exposure to Air and Dust

Contact with air and dust introduces microbial contaminants to distilled water, seeding it with bacteria. Studies find up to thousands of bacteria per liter of distilled water exposed even briefly to air. Piped distribution systems and stirring during storage facilitate airborne contamination.

Temperature Changes

Heating distilled water can select for thermophilic bacteria, while cooling promotes growth of psychrotrophs. Stagnant water also adopts ambient temperature, providing more hospitable conditions for mesophiles. Temperature gradients within storage tanks provide diverse microenvironments.

pH Changes

Absorption of carbon dioxide from air acidifies distilled water over time, while leaching of minerals from piping raises pH. Even marginal pH changes significantly influence microbial communities. Acidic conditions favor acidophiles like Acetobacter.

Piping Materials

Leaching of minerals and metals from piping materials can augment the mineral content of distilled water. Iron, copper, zinc, and other metals liberated from pipes may serve as essential nutrients for bacterial growth. However, some metals are antimicrobial at high doses.


Stagnant distilled water allows episodic nutrient spikes to persist rather than being flushed away under flow conditions. With food available, standing water enables microbial colonizers to establish stable populations rather than being washed out by flow.

Biofilm Formation

By adhering to wet surfaces, bacteria create protective biofilms with access to nutrients leaching from pipes. Within biofilms, bacteria are sheltered from disinfectant residuals present in distilled water. Biofilms act as persistent sources of microbial contamination.

Water Age

The longer distilled water remains in storage, the more opportunities exist for nutrient levels to increase, temperature changes to occur, biofilms to develop, and bacteria to gain footholds. Regular flushing and turnover of stored distilled water helps curtail microbial growth.

How Long Until Bacteria Appear?

Bacteria can begin colonizing distilled water remarkably quickly under favorable conditions:

– Within hours, airborne bacteria settle into exposed water along with traces of dust and nutrients.

– Over days, pioneers attach to surfaces and incubate biofilms, providing a beachhead.

– Within weeks, increasing nutrients allow biofilms and free floaters to flourish.

– Given months, rich microbial ecosystems develop in stagnant systems.

Exact timelines depend heavily on extrinsic factors like water handling, storage tanks, and ambient contamination levels. However, the underlying premise is that bacteria exploit any available niche quickly. Maintaining purity requires constant vigilance.

Does Distilled Water Go Bad?

Distilled water itself does not go bad or expire like milk or food does. However, over time, distilled water can become contaminated with bacteria and take on unpleasant odors, colors, and tastes.

Here are signs that your distilled water has gone bad:

  • Cloudiness or sediment – Particles clouding the normally clear water.
  • Strange smell – An earthy, musty, or rotten odor.
  • Off tastes – Bitter, sour, or unpleasant flavors.
  • Discoloration – A yellow, brown, or greenish tinge.
  • Bacterial growth – Slime, sheen, or fuzziness on the water’s surface.

While not directly harmful, these are red flags that your distilled water is contaminated. At this point, it is best discarded and replaced with a fresh batch. Frequent replacement helps prevent bacterial growth and buildup of organic compounds.

How to Store Distilled Water

Proper storage is key to maintaining purity and inhibiting bacterial growth in distilled water over time:

  • Use sterile, sealed glass, stainless steel, or food-grade plastic containers. Avoid reactive metals.
  • Fill containers completely to the top to minimize air exposure.
  • Refrigerate or freeze water if stored for more than a few days.
  • Clean containers thoroughly before refilling to remove biofilms.
  • Limit light exposure which facilitates algal growth.
  • Rotate stock to use oldest water first following FIFO (first-in, first-out).

Container choice, temperature, turnover rate, and handling technique all influence how long distilled water stays pure before bacteria inevitably appear.

How to Disinfect Distilled Water

To destroy any bacteria accumulating in distilled water, additional disinfection steps may be warranted:


Re-boiling stored distilled water kills vegetative bacteria by exposing them to 212°F (100°C) temperatures. However, endospores may survive.

UV Irradiation

Ultraviolet light disrupts microbial DNA, preventing replication. Effective for eliminating bacteria, viruses, and protozoa.


Passing water through 0.2 micron filters removes most bacteria based on size exclusion. May leave some viruses and endotoxins.


Ozone gas bubbled through water damages bacterial cell walls, membranes, and intracellular contents. Leaves no residue.

Chemical Disinfection

Halogens like chlorine, iodine, and bromine kill microbes and provide residual disinfection but may be undesirable in end uses.

Ionizing Radiation

Exposing water to gamma rays or electron beams from Cobalt-60 or accelerators sterilizes by shredding microbial DNA but requires specialized equipment.

Depending on application, periodic disinfection using appropriate methods keeps distilled water free of pathogenic bacteria.

Uses of Distilled Water

Here are some common uses of distilled water and concerns about bacteria:

Drinking Water

Lack of minerals makes distilled water a poor everyday drinking water. Flat taste, and potential bacteria growth with storage make it unsuitable for hydration. However, short-term drinking is not hazardous for healthy adults. Those with compromised immunity should take precautions against distilled water bacteria.

Medical and Scientific Uses

Hospitals, labs, pharmaceutical plants, and other facilities need high purity distilled water. Bacteria could alter water chemistry, influence experimental results, or contaminate products and processes. Strict protocols limit bacterial levels for medical-grade distilled water.


Many recipes call for distilled water to avoid mineral tastes or reactions. While bacteria are not a large concern for casual cooking, growth during storage could impart off-flavors. Those with hypochlorhydria should properly disinfect distilled cooking water.

Batteries and Coolants

Distilled water sees wide use as battery fluid, coolant, and other industrial applications where mineral buildup is problematic. However, unchecked bacteria may degrade performance. Periodic biocide addition helps control microbes in these systems.

Humidity Control

Ultrasonic humidifiers vaporize distilled water to avoid mineral dust. But bacterial accumulations get aerosolized along with water droplets, posing an inhalation hazard. Proper humidifier sanitation and using boiled water minimizes risks.

Other Sensitive Uses

Photo development, electronic manufacturing, cosmetics, and plastics manufacturing often require distilled water to avoid chemical reactions or precipitation. Bacteria can ruin these sensitive processes, so sterile water is essential.

The impacts of bacterial contamination vary across uses, but potentially disruptive. Matching water quality to appropriate end uses prevents problems.

Should You Drink Distilled Water Every Day?

Daily drinking of distilled water is discouraged:

  • It lacks essential minerals like calcium, magnesium, and potassium needed for good health.
  • Distilled water leaches minerals from the body over time.
  • Frequent mineral deficits can lead to electrolyte imbalance, fatigue, heart abnormalities, and bone density loss if sustained long-term.
  • The aggressive hydrating qualities of distilled water may dislodge toxins stored in tissues.
  • Potential bacterial growth during storage raises infection risks.

Occasionally drinking small amounts of distilled water is not harmful. However, it is a poor everyday drinking water source given its biological and mineral characteristics. Most experts recommend against relying on distilled water for regular hydration.

Is It Safe to Drink Old Distilled Water?

Drinking distilled water stored for long periods carries some risks:

– Old distilled water may contain multiplied bacteria that can cause disease. Opportunistic pathogens are especially concerning for those with impaired immunity.

– Chemical changes over time degrade water quality. Absorption of gases and leaching of piping materials alter water composition.

– Off-tastes indicate organic contamination that while not directly harmful, signals the water is no longer pure.

– Stale flavor makes old distilled water unpalatable for drinking anyway.

The lack of minerals in distilled water mean it does not “go bad” per se. But physical, chemical, and especially microbial changes do occur with storage time, making old water unfit to drink. Stored distilled water is best used for non-potable purposes.

Does Distilled Water Go Bad in a Car?

Yes, distilled water in a car can go bad due to:

– High temperatures inside hot parked cars accelerate bacterial growth, especially in summer.

– Large temperature fluctuations from frigid nights to hot days enrich diversity of microbes.

– Stagnant conditions allow biofilms and metabolites to accumulate once fluid levels drop.

– Leaching of minerals from tubing and cast metal components elevates nutrient levels.

– Exposure to dust/dirt during radiator filling and from cabin air introduces more bacteria.

– Long static hold times between draining/refilling allow greater microbial proliferation.

Within weeks to months, distilled water in car cooling systems can become foul, discolored, and loaded with bacteria. Annual flushing helps counteract this, along with biocide additives in the radiator.


In summary, distilled water provides an unfavorable environment for most bacterial growth due to its low nutrient levels. However, distilled water is not guaranteed sterile. Various factors can enable bacteria to establish populations in distilled water over time. Proper handling, storage, turnover, and periodic disinfection are needed to control microbial contamination. While occasional drinking carries low risks for healthy adults, long-term consumption of distilled water as an everyday drinking source is not recommended. Vigilance is required to maintain adequate purity for sensitive medical, scientific, and industrial uses.

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