I was visiting my sister in Baltimore over the weekend when I saw this really cool lighthouse known as the Seven Foot Knoll. Obviously, it is not in use anymore and has been moved to shore to preserve it as a historical sight, but it used to sit out in the water at the mouth of the Patapsco River. When the lighthouse was in use the light keeper and his family had to live inside of it for long periods of time because there wasn't any easy access to land. They would take everything they needed out with them, including livestock and food supplies. For drinking water the lighthouse funneled rainwater from the roof into 2 large cisterns.
The biggest problem with collecting the rainwater from the roof was the lead that was washed into the cistern with it. Salt spray from the ocean caused the lead roof of the lighthouse to corrode so when it rained the lead mixed with fresh rainwater and contaminated the cistern. Lead is highly toxic and is one of the contaminants that you really don't want in your drinking water. To neutralize the lead they added powdered chalk to the collected water. Fortunately, modern filters are far more effective at reducing lead, but in 1902 it was a standard practice for the light keeper and his family to add chalk to the water.