Water runoff occurs when excess water flows over land picking up contaminants and depositing them into bodies of water. This nonpoint source pollution is now the primary cause of water quality issues in the US, with 40% of surveyed waters considered unsafe. Some solutions to lessen water runoff include using porous paving that absorbs water, installing rain barrels to collect roof runoff, creating rain gardens to filter runoff, and implementing filters of various kinds. Simple individual actions like composting yard waste and sweeping instead of hosing can also help.