Avoid the water to contact the wooden part of whistle: try not to turn fujara upside down, keep it in straight position if possible.
Use the cork below the mouthpeice of fujara to take out the water.

If accidentally water contacted the wooden part of the whistle and sound bacame weak or loses the high overtones, let the wooden part to dry out for one or two days, then sound will come again.

this is very simple rule, easy to follow. I had this problem only once with one of my fujaras. Then i started to follow this rule and never had the same problem again.