So you've run your tap and instead clear water, it is coming out the tap as brown water or yellow water. This maybe nothing or a sign of trouble, below is some helpful advice.
Work being taken out in the local area may cause water to become discoloured for awhile, so check with your local supplier. This can easily be confirmed by checking with a neighbour to see if they have the same problem.
Wait awhile before using your water, as this will give the supply a chance of clearing the problem. Don't drink the water, bath or wash anything with the water(clothes or food ) until back to normal. However it is safe to use the water to flush the toilet.
If you have checked with your supplier and neighbour and they are not aware of any problem. Or you may have had some workdone recently, then the problem may be in your home. It maybe that your hotwater is being contaminated by your heating (where the coil in your cylinder is leaking or someone has accidently added inhibitor to a primatic cylinder). It could even be the lid being left off a water tank, allowing debris into the system.
As above you shouldn't use the water to drink, bath or wash until the problem is fixed. You may find draining down the system and refilling clears your problem. However you should get a local engineer to check this out as anything sinister isn't easy to check yourself.
Cloudy White Water
This is common, you run the tap it seems really white and cloudy, then after a few seconds clears up. Cloudy water, also known as white water, is caused by air bubbles in the water. It is completely harmless If yours stays white then contact your local water supply company.