The impulse to use water for quick relief from dry, irritated eyes is understandable due to its universal accessibility. Dry eye disease causes discomfort from a lack of tear production or quick tear evaporation. While tap water may seem like a harmless, immediate solution, its chemical and physical properties make it strongly discouraged and potentially harmful for ocular use. Safe alternatives, including specialized over-the-counter products and simple behavioral adjustments, offer far better and safer long-term relief.
The Direct Answer: Why Tap Water Is Harmful
Tap water is not sterile and poses several threats to the delicate balance of the eye’s surface. A primary concern is its osmolarity, which is the concentration of dissolved salts and minerals. Healthy human tears are isotonic, maintaining an osmolarity of approximately 300 milliosmoles per liter (mOsm/L).
Tap water, in contrast, is hypotonic, meaning it has a much lower salt concentration than tears. When hypotonic water contacts the eye, osmosis causes water to rush into the corneal cells to balance the salt concentration. This cellular swelling causes irritation, strips the protective lipid layer of the tear film, and can worsen the underlying dryness.
Tap water also contains contaminants. Municipal water supplies are often treated with chlorine, a known irritant that can cause burning and redness. The water may also contain trace minerals and microorganisms, including the parasite Acanthamoeba. This parasite can cause a rare but devastating eye infection called Acanthamoeba keratitis. This infection is particularly dangerous for contact lens wearers, as the parasite can become trapped between the lens and the cornea, potentially leading to vision loss.
The pH of tap water can also contribute to discomfort. Healthy tears have a neutral pH, typically ranging from 7.0 to 7.6, but tap water can be slightly alkaline, often with a pH of 7.5 or higher. This difference in acidity can disrupt the eye’s natural environment, leading to stinging and worsening the sensation of dryness.
Effective Over-the-Counter Alternatives
Instead of tap water, the safest first step for relief is using over-the-counter artificial tears. These products are formulated to mimic the physical and chemical properties of natural tears, containing ingredients like demulcents (lubricants such as carboxymethylcellulose or hyaluronic acid) and stabilizers. A basic saline wash is sterile and isotonic, but it is only meant for rinsing irritants and lacks the necessary lubricating agents to treat dry eye effectively.
Artificial tears are available in various viscosities, allowing for treatment tailored to the severity of symptoms. Thin, watery drops are ideal for mild or occasional dryness and cause minimal visual blur, making them suitable for daytime use. Thicker gels and ointments offer longer-lasting lubrication but can temporarily blur vision. These viscous formulations are recommended for moderate to severe symptoms or for overnight use.
Patients who use artificial tears frequently (more than four times per day) should choose preservative-free options. Standard multi-dose bottles contain preservatives like benzalkonium chloride (BAK) to prevent bacterial growth. However, with repeated use, these chemicals can become toxic to the eye’s surface. Preservative-free drops, often packaged in single-use vials, eliminate this risk and are gentler for long-term use.
Essential At-Home Management Strategies
Complementing the use of artificial tears with non-drop strategies can significantly improve dry eye comfort. Warm compresses are an effective measure for evaporative dry eye. Applying a warm compress for 5 to 10 minutes helps to soften and melt the thickened oil (meibum) that clogs the meibomian glands along the eyelid margins. The optimal temperature for the compress should be around 40 to 41.5°C to stabilize the tear film’s lipid layer.
Behavioral adjustments during screen time are also beneficial, as prolonged focus reduces the natural blink rate from 15-20 blinks per minute down to as few as 5-7. The “20-20-20 rule” is a simple practice: every 20 minutes, look at something 20 feet away for 20 seconds. This helps relax the focusing muscles and encourages conscious, complete blinking, which spreads a fresh layer of tears across the ocular surface.
Controlling the environment can reduce tear evaporation, especially in dry climates or air-conditioned spaces. Using a humidifier to maintain indoor humidity levels between 40% and 60% can slow the rate at which tears dry up. Systemic hydration is also important. Additionally, the intake of essential fatty acids, such as Omega-3s (EPA and DHA), supports the quality of the tear film’s oil layer due to their anti-inflammatory properties.