Niagara's Leak Detection Toilet Dye Tablets are used to rapidly identify a leaky toilet tank which can waste thousands of gallons of water per year. Damaged flappers can leak water undetected down your drain. Simply place Niagara's Leak Detection Dye Tablets into your toilets tank, and if blue water appears in your bowl, you have a damaged flapper that needs to be replaced. Niagara's Dye Tablets are non-toxic and include easy to follow bi-lingual directions.