Certain times of the year when there is less rainfall, the hardness in the water is higher because there has been no rainfall to dilute the minerals in the river. This hardness can settle out in the plumbing in the form of a white or tan residue. Hardness is calcium carbonate and is a substance that is beneficial to the human body. Deposits can be removed with vinegar or a water softener can be installed to remove the calcium carbonate. A high hardness content can sometimes form an oily appearing film on the top of the water.