If a few micrograms of mercury can contaminate 7000 gallons of water, then you should worry. Otherwise, it may be reasonable to believe that’s hype from the LED-making company.
1 gallon of water weighs 3.8 Kg.
The EPA standard for mercury in drinking water is no more than 2 parts per billion.
Each CFL contains about 5 milligrams of Mercury.
So, that is 5 milligrams diluted into 2.5 billion miligrams of water, or 2.5 million grams, or 2,500 Kg of water.
2,500 Kg of water is about 660 gallons.