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.
Rainwater is known to have acidic properties that can negatively affect your pool water chemistry balance. This can affect anything from the pH balance to alkalinity levels and more. The pH of rain across the US, which is all acid rain, is due to industrial gasses (i.e. NOx, SOx) which make nitric and sulfuric acid. Aside from rainwater falling directly into your pool being a bad thing, something even worse can happen.