Turning on the faucet and seeing milky or white water often raises immediate questions about its purity. This temporary cloudiness, frequently described as white water, is almost always a physical phenomenon caused by dissolved air in the water supply. The appearance is largely aesthetic and typically signals no issue with water quality.
The Primary Cause: Trapped Air Bubbles
The milky appearance of tap water stems from a simple principle of physics involving pressure and gas solubility. Water delivered through municipal systems is kept under significant pressure to ensure it reaches every location. This increased pressure forces atmospheric gases to dissolve into the water at concentrations higher than normal.
When the water leaves the pressurized pipe and flows out of a faucet, the pressure abruptly drops to normal atmospheric levels. This sudden release causes the excess dissolved gas to escape the liquid solution, forming millions of minute air bubbles. These micro-bubbles scatter light, which gives the water its opaque, white coloration. This effect is often more noticeable with cold water because lower temperatures permit water to hold a greater volume of dissolved gas.
Performing the Simple Clarity Test
Determining whether the cloudiness is harmless air or a different matter can be done with a quick, two-minute observation. Begin by filling a clear glass directly from the tap that shows the white water. Watch the glass without disturbing the water surface.
If the cloudiness is due to trapped air, the water will begin to clear within a minute or two. The clearing process happens from the bottom upward as the tiny, buoyant air bubbles rise to the surface and dissipate. If the water returns to a clear state within this short timeframe, it confirms the cause was aeration and the water is safe to drink.
When Cloudiness is Not Air
While air bubbles account for the vast majority of cases, cloudiness that persists beyond a few minutes may indicate the presence of suspended solids. A common non-air cause is mineral sedimentation, which occurs particularly in areas with hard water rich in calcium and magnesium. These minerals can precipitate out of the solution and remain suspended, giving the water a persistent cloudy look.
Cloudiness that does not clear or is accompanied by a distinct color tint suggests the presence of other particulate matter. Brown, yellow, or reddish water may contain rust or iron sediment from aging internal plumbing or the water main. White cloudiness that remains opaque could be caused by silt, clay, or total suspended solids (TSS) that entered the system after a pipe repair or disturbance. If the water fails the simple clarity test, contacting the local water utility to investigate the source is the next step.