Can you use water instead of saline?

October 10, 2025 •

4 min read

Tap water in the United States is treated to safe drinking standards, but low levels of microorganisms remain [1.4.1]. This raises a critical question for home and medical use: can you use water instead of saline solution safely and effectively?

Quick Summary

Using water instead of saline depends entirely on the application. While tap water may be suitable for cleaning some acute wounds, using it for nasal rinsing, eye care, or with medical devices carries significant infection risks.

Key Points

Tonicity is Key: Normal saline is isotonic, matching the body's salt concentration and preventing cell damage, while plain water is hypotonic and can cause cells to swell and burst [1.5.2, 1.7.3].
Tap Water is Not Sterile: While safe for drinking, tap water contains microorganisms that can cause serious infections in wounds, sinuses, or eyes [1.4.1, 1.4.4].
Nasal Rinsing Danger: Never use untreated tap water for nasal irrigation due to the risk of fatal brain infections from amoebas like Naegleria fowleri [1.3.2, 1.11.1].
Eye and Contact Lens Safety: Only use commercially prepared sterile solutions for contact lenses and eye flushing to prevent infections like Acanthamoeba keratitis [1.10.1, 1.10.4].
Wound Care Exception: For minor, acute wounds, some studies show tap water can be as effective for cleansing as saline, but saline remains the standard, especially for chronic wounds [1.2.2, 1.2.3].
Medical Devices: Always use distilled or sterile water in devices like CPAP machines and humidifiers to avoid inhaling harmful waterborne pathogens [1.4.3, 1.4.4].
DIY Saline: Homemade saline for nasal rinsing must be made with distilled, sterile, or previously boiled water and non-iodized salt [1.3.1, 1.8.2].

Understanding the Core Difference: Tonicity and Sterility

When considering if water can replace saline, two concepts are paramount: tonicity and sterility. Normal saline is a sterile mixture of 0.9% sodium chloride in water [1.5.1, 1.6.2]. This specific concentration makes it an isotonic solution, meaning it has a similar concentration of solutes to human blood and cells [1.6.1, 1.7.3]. This balance is crucial because it prevents damage to tissues; fluid does not excessively rush into or out of cells [1.7.3].

Water, on the other hand, is hypotonic. It has a much lower solute concentration than human cells [1.7.3]. When plain water comes into contact with cells, such as in an open wound or nasal passage, osmosis causes water to rush into the cells, causing them to swell and potentially burst [1.5.2, 1.7.3]. This process can cause a burning sensation, irritation, and tissue damage [1.3.4, 1.3.5].

The second major difference is sterility. Medical-grade saline and sterile water are treated to remove all microorganisms [1.5.1]. Tap water, while safe to drink because stomach acid kills most germs, is not sterile [1.4.4, 1.3.5]. It contains low levels of microorganisms like Pseudomonas, Legionella, Acanthamoeba, and Naegleria fowleri [1.4.1, 1.4.4]. While harmless when ingested, these microbes can cause severe, and sometimes fatal, infections if introduced into wounds, sinuses, or the eyes [1.4.1, 1.11.1].

Comparison: Water vs. Saline Solution


Feature	Saline Solution (0.9% Normal)	Water (Tap, Distilled, Sterile)
Tonicity	Isotonic (matches body fluids) [1.6.1]	Hypotonic (tap/distilled) or Isotonic (if salt is added) [1.7.3]
Effect on Cells	No net fluid shift, gentle on tissues [1.7.3]	Causes cells to swell and potentially burst (lysis) [1.5.2]
Sterility	Commercially prepared is sterile [1.5.1]	Tap water is not sterile [1.4.1]. Sterile water is sterile. Distilled water is not necessarily sterile [1.5.1].
Composition	0.9% sodium chloride (salt) in purified water [1.6.2]	H₂O, may contain minerals and microorganisms (tap) or be purified (distilled/sterile) [1.4.1, 1.5.1].
Common Uses	IV fluids, wound irrigation, nasal rinses, eye flushing, contact lens care [1.6.2, 1.6.3]	Wound cleaning (limited cases), diluting medications (sterile water), home nasal rinse base (boiled or distilled) [1.5.1, 1.3.1].

Specific Use Cases: When is Water an Option?

Wound Cleansing

For acute, minor traumatic wounds, some evidence suggests that clean, potable (drinkable) tap water is as effective as sterile saline for cleansing [1.2.2, 1.9.3]. One systematic review even found a significant reduction in infection rates for acute adult wounds cleaned with tap water compared to saline [1.2.2]. However, this is debated, and other evidence is of low certainty [1.2.3]. For chronic wounds or wounds with exposed bone or tendon, normal saline is generally recommended [1.2.3, 1.2.5]. Using a whirlpool or water under pressure is not recommended as it can drive bacteria into the tissue [1.2.1].

Nasal Irrigation (Neti Pots and Rinses)

Never use untreated tap water for nasal irrigation [1.3.2, 1.3.5]. Doing so carries a risk of introducing dangerous amoebas like Naegleria fowleri or Acanthamoeba into the sinuses, which can travel to the brain and cause rare but deadly infections [1.3.2, 1.11.1, 1.11.2]. For sinus rinsing, you must use one of the following:

Distilled or sterile water (store-bought) [1.3.1].
Tap water that has been boiled for at least one minute (three minutes at high elevations) and then cooled to a lukewarm temperature [1.3.1].

Once you have safe water, you can create a saline solution at home. A common recipe involves mixing non-iodized salt and baking soda into the prepared water [1.3.3, 1.8.2]. Rinsing with plain water without the salt mixture will cause a severe burning sensation [1.3.4].

Contact Lenses and Eye Care

Never use any type of water—tap, distilled, or homemade saline—to clean, rinse, or store contact lenses [1.10.1, 1.8.1]. Tap water can contain the microorganism Acanthamoeba, which can adhere to lenses and cause Acanthamoeba keratitis, a painful and sight-threatening eye infection [1.10.2, 1.10.4]. Always use commercially prepared, sterile contact lens solutions. For flushing debris from the eye itself, only sterile saline eyewashes should be used [1.8.1].

Medical Devices (CPAP, Humidifiers)

Similar to nasal rinsing, tap water should not be used in medical devices like CPAP machines or humidifiers [1.4.3, 1.4.4]. The aerosolized water can carry pathogens like Legionella and Pseudomonas into the lungs [1.4.3]. Use distilled or sterile water as per the manufacturer's instructions [1.4.4].

Conclusion

While it seems like a simple substitution, the choice between water and saline has significant implications for safety and effectiveness. Saline's key advantage is its isotonic nature, which makes it gentle on human tissues, preventing the cell damage that hypotonic water can cause [1.5.2]. For most medical applications—including nasal rinsing, eye care, contact lens use, and IV fluids—sterile saline is the required standard due to both its tonicity and sterility. Using unsterilized tap water in these situations introduces a risk of severe infections [1.3.2, 1.10.1]. The only area where tap water may be an acceptable alternative is in the initial cleansing of minor, acute wounds, though saline remains a favored and universally safe option [1.2.3, 1.9.3]. When in doubt, sterile saline is the medically sound choice.

For more information on safe sinus rinsing, consult the CDC's guidance on Naegleria fowleri [1.3.1].

Frequently Asked Questions

Saline solution contains 0.9% sodium chloride (salt), making it isotonic with body fluids, while sterile water is pure, purified water with no additives [1.5.1]. This salt content in saline prevents it from damaging cells, which sterile water can do through osmosis [1.5.2].

For minor, acute wounds, evidence suggests drinkable tap water is often as safe and effective for cleansing as sterile saline [1.2.2, 1.9.3]. However, for chronic wounds or deep injuries, saline is preferred [1.2.5].

No, you should never use untreated tap water in a Neti pot. It can contain dangerous microorganisms that may cause a rare but fatal brain infection [1.3.1, 1.11.1]. Always use distilled, sterile, or previously boiled and cooled water [1.3.1].

Tap water is not sterile and can harbor microorganisms like Acanthamoeba. Rinsing your lenses with water can lead to a severe, painful eye infection called Acanthamoeba keratitis, which can threaten your vision [1.10.1, 1.10.4].

Injecting a large amount of sterile (hypotonic) water intravenously is dangerous. It would cause water to rapidly enter red blood cells, leading them to rupture (hemolysis), which can have lethal consequences [1.5.2, 1.5.5].

To make a safe solution for nasal rinsing, mix 1 teaspoon of a pre-made dry mixture (3 parts non-iodized salt, 1 part baking soda) into 8 ounces of lukewarm distilled, sterile, or previously boiled water [1.3.5, 1.8.1].

No. Distilled water is purified by distillation to remove minerals and impurities, but it is not necessarily sterile (free of all microbes). Sterile water has been treated specifically to eliminate all microorganisms [1.5.1].