Can rotting wood in water cause health problems?

Long story short.. I rent a house and after a bit of trouble with my water cylinder I foudn out that the top of the cylinder was made out of a concreate slab and wood. The wood had rotted and fallen into the cold water bit of the water cylinder, which we obviously use for drinking and washing. When we told the letting agents they weren't too bothered. However I have suffered with an upset stomach on a regular basis - could the two be connected? If so what do you suggest I do with teh letting agents?