When you turn on your faucet and the water comes out white, milky or cloudy, it can set off warning bells. There are a few causes of cloudy water. Some are harmless, but others can pose health threats if not treated. We’ve broken down some of the major signs, causes, and solutions for cloudy water.

One of the most common causes of cloudy water is air bubbles. Fortunately, air bubbles rise, so if your water begins cloudy and clears from the bottom up, it’s a good way to test that you just have extra air trapped in your water.

These cloudy air bubbles are completely harmless. They are most common when the temperature is cold outside because more air dissolves into cold water than warm water.

Air is also more soluble with higher water pressure, so any increase in air pressure can cause air bubbles. Recent plumbing work, too, can increase the amount of air trapped in your water.

If you leave your water to sit in an open glass or container, then the air bubbles will naturally rise and dissipate, and you’ll have a clear glass of water in no time.

Another common cause of cloudy water is sediment. Unlike air bubbles, your cloudy water will not clear with time if it’s full of sediment. Your water may look dirty, or it may look like things are moving in your glass.

Total suspended sediment (TSS) is a measure of the concentrations of small particles in your water. High TSS can be caused by runoff into the water supply or recent disturbances—such as drilling, construction, or major storms—near your well or your city’s water source.

Sediment is not always a huge cause for health concern, but high concentrations of solids can lead to bacteria growth. Toxicants can also cling to these particles, getting into your drinking water as well. The EPA has no specific guidelines on safe levels of TSS, but it’s generally good practice to know what’s in your water to be sure TSS aren’t associated with bacteria or other toxicants.

Low levels of sediment can often be cleared with a simple water filter. In some cases of extreme cloudiness and lots of solids, multi-level media filtration is necessary.

A rarer—and more dangerous—source of cloudy water is methane gas. In higher levels, this one is easy to spot. If your water makes sputtering or bubbling noises as it comes out, spurts out, or contains white bubbles, you may have dissolved methane gas.

If you think you have methane gas in your water, one of the first steps to take is to make sure that the area is very well ventilated when you turn on the faucet, run the washing machine, or turn on the dishwasher. Methane gas is flammable and usually odorless. So though dangerous, it is often difficult to detect if you’re not looking for it.

There's a higher chance of finding dissolved methane if you use a private well. If you have signs of methane, you should test your well water straight away.

Of course, the level of methane matters. The US Department of Interior set out guidelines for safe dissolved methane concentrations. Concentrations that measure less than 10 parts per million (PPM) are considered unproblematic. Other than routine monitoring, these levels require no action. If you have more than 10 PPM but less than 28 PPM of dissolved methane, removing anything potentially flammable from the area is recommended. Beyond that, the Department of Interior and other experts recommend monitoring and potentially treating your water.

If you have over 28 PPM, your well should be immediately vented and your water immediately treated to lower methane levels.

“Hard” water may seem like an oxymoron, but it can be very common depending on where you live. Signs of hard water are greyish-white films on sinks and dishes and less suds in laundry or when using soap. Hard water isn’t considered a health hazard. If water hardness causes any issues, it is usually aesthetic–e.g. taste or staining on clothing–or plumbing and appliance related.

What makes water hard, you ask?

Hardness comes from minerals like calcium and magnesium dissolved in rocks. Again, concentration matters. Levels of calcium and magnesium compounds that are 0 to 60 PPM of calcium carbonate are classified as soft. 61 to 120 PPM is moderately hard, 121 to 180 PPM is hard, and over 180 PPM is very hard.

The likelihood of having hard water varies significantly by region, too. According to a US Geological Survey map updated in 2005, the east coast — excluding some cities, such as Baltimore — generally has softer water, while places like Texas and Southern California have some of the hardest water.

Ion-exchange filters, which exchanges calcium and magnesium for potassium or sodium, can help soften water.