Which of the following can help reduce indoor potable water use?

Composting toilets are particularly effective at reducing indoor potable water use because they eliminate the need for water-based flushing systems altogether. Unlike traditional toilets that rely on a significant amount of fresh water to operate, composting toilets use a dry system to manage human waste, allowing for complete waste decomposition and minimizing water consumption. This leads to substantial reductions in the overall demand for indoor potable water.

While dual-flush toilets can also lower water use by offering two flushing options, they still require some water to function. Graywater systems recycle wastewater from sinks and showers for non-potable uses, which helps reduce overall potable water needs but doesn't directly decrease inside use of water. Traditional cisterns can be beneficial for collecting rainwater for outdoor use, but they do not primarily address indoor water consumption. Thus, composting toilets represent the most effective measure among the options for reducing indoor potable water use directly.