Cloudy water, scientifically referred to as turbidity, is a measure of the degree to which water loses its transparency due to the presence of suspended matter. This cloudiness occurs when tiny particles scatter light, giving the water a hazy or milky appearance. Turbidity is a common occurrence that affects both tap water and natural bodies of water, with causes ranging from the harmless presence of gas to physical, chemical, or organic contaminants.
The Simplest Explanation: Dissolved Air
The most frequent cause of temporary cloudiness in tap water is the presence of microscopic air bubbles, resulting in a milky-white appearance when water is first drawn from a faucet. This phenomenon is governed by the solubility of gas in liquid, which is affected by temperature and pressure.
Water that is cold and under pressure, such as that traveling through underground pipes, holds more dissolved air. When the pressurized water leaves the faucet, the sudden drop in pressure causes the excess dissolved air to rapidly come out of solution. This immediate release forms a dense cloud of tiny bubbles, similar to the action seen in a carbonated drink.
Aeration can be more pronounced in colder months because cooler water holds a greater volume of dissolved air. If the water is subsequently heated, the solubility decreases further, causing the air to release as bubbles. This common type of cloudiness will clear quickly, with the bubbles rising and dissipating within a minute or two.
Physical Causes: Sediment, Silt, and Rust
Cloudiness that is persistent and does not dissipate quickly is caused by solid, non-dissolved particles suspended in the water. These physical contaminants, collectively called sediment, include materials like clay, silt, sand, rust flakes, and scale. Their size and density cause them to hang in the water column or settle slowly.
These solid particles enter the water supply through disturbances. In municipal systems, events like water main breaks, construction activities, or the use of fire hydrants can stir up settled sediment. For homes using well water, heavy rainfall or changes in groundwater conditions can introduce fine particles.
The appearance of the cloudiness often indicates the specific type of sediment. Rust, which is iron oxide flaking off corroding pipes, typically gives the water a reddish, orange, or brown tint. Sediments like clay and silt generally result in a grayish or brown murkiness. Unlike air bubbles, these suspended solids will cause particles to settle at the bottom of a glass if left undisturbed.
Chemical Reactions and Organic Growth
Cloudiness can also originate from chemical processes or the proliferation of living organisms. Chemical precipitation occurs when dissolved minerals solidify into tiny, suspended particles. This is common in hard water areas with high concentrations of minerals like calcium and magnesium.
These minerals can react with disinfectants, temperature changes, or pH changes, causing them to precipitate out of the solution and form a persistent, milky haze. Iron and manganese are other common dissolved metals that oxidize, creating visible precipitates that result in gray, black, or reddish-yellow discoloration and cloudiness. This chemical cloudiness often requires specific water treatment.
Cloudiness can also be biological, stemming from organic growth such as algae or bacteria. Algae blooms, often triggered by excess nutrients and light, typically result in a distinct green tint. Bacterial growth causes a milky-white or grayish cloudiness, often occurring with an increase in organic matter, such as in private wells. These organic causes may also be accompanied by a noticeable odor or a slimy film.
How to Identify the Cause and When to Take Action
Determining the source of cloudiness is the first step toward resolution. A simple at-home observation, often called the “glass test,” provides immediate clues. To perform this test, fill a clear glass with the cloudy water and place it on a flat surface. If the cloudiness begins to clear rapidly, from the bottom of the glass upwards, the issue is harmless dissolved air.
If the cloudiness remains for several minutes, or if particles begin to settle, the cause is suspended solid matter like silt, rust, or mineral precipitates. Observing the color can further narrow down the cause, with brown or red suggesting rust, and green pointing toward algae.
Cloudiness caused by air is benign and requires no action. However, persistent cloudiness caused by sediment, chemical discoloration, or biological growth requires attention. For public water customers, reporting a persistent issue to the utility company is the appropriate step, as they can perform testing and address infrastructure problems. For well water users, professional water testing is advisable to identify the exact contaminant and determine the necessary filtration or treatment system.