If you have a cold or had a cold virus and the nose mucus was running a different color such as yellow and then suddenly the nose mucus is running clear liquid then it likely is a good sign that the cold virus is clearing up.
Usually when I have a cold I have a lot of yellow snot coming out of my nose and then when the cold virus is clearing up I start having clear liquid coming out of my nose.
Also if you have allergies your nose could also run clear liquid until the allergies go away.
If the nose continues to run clear liquid then it could be some other health issue such as brain drainage which is not too good of a thing and you should see a doctor about it.
The runny nose running clear liquid could just be excess nasal drainage as well and most times the clear liquid coming out of your nose is nothing to worry about.