Sometimes water can look milky or cloudy because it contains tiny bubbles of air. Air is always in water, but it can be more obvious after it has travelled through the mains, if there is a burst mains pipe or if a faulty plumbing fitting has been used.
As well as the change in how it looks, you may also notice knocking or banging noises coming from the internal plumbing.
To check if this is the problem, run a glass of water and allow it to stand for a few moments - the cloudiness should clear from bottom to top. To help fix this, you can try running the cold water tap at the first point of entry in to the property (closest to the internal stop tap) on a slow steady flow. While the tap is running, turn the internal stop tap on/off 4-6 times to help release the air from the pipes.
Cloudy water caused by tiny air bubbles in the water is not harmful to health.
If you've tried this but are still concerned, or you'd like more advice you should contact your water supplier.