I noticed that my serpentine belt started to chirp, i sprayed some water on the grooved side, and stopped the chirping for a while, but later started again.

Can this be the belt, or the tensioner?

Here, i made a video what exactly happening.

 

https://www.youtube.com/watch?v=5te12uVAT8E

Most probably just glazed from age and dust etc.

 

I've found pouring a couple of litres of very hot water with laundry detergent on the inner ribbed surface whilst the engine is running then rinsing with a garden hose works to clean up the belt and stop the noise.

 

The only real cure is a new belt 

I think Gater recommend a new one every 4-5 years but that@s overkill(usually)  as they wear they run on the base of the grooves instead of biting on the micro V's   a good chance to check the tensioner pully bearing (and grease if necessary)  while it's  off