national monument. noun. Definition of national monument for English Language Learners. : a place (such as an old building or an area of land) that is owned and protected by a national government because of its natural beauty or its importance to history or science. Britannica.com: Encyclopedia article about national monument.
Brown or discolored water is caused by minerals, sediment, or rust that may accumulate in the water mains over time. When the water from your tap is brown this indicates a disturbance in the water main that stirs up these deposits.
There are three causes of green pool water. The first is a lack of chlorine. Without chlorine the pool water will quickly start to grow algae and turn green. Water without chlorine, especially if it has an algae bloom, is unsafe to swim in, and can be a breeding ground for mosquitoes and other insects. The second thing that causes pool water to look green (or yellow) is pollen.