In most of takings law, legal precedent requires a full "taking" of private property. This means the government has either rendered a piece of private property null of all value to the owner, or the government has outright taken possession of the property. According to the 5th Amendment of the United States Constitution, a taking also requires the government to compensate the private property owner for the loss of value, or the loss of the property.
However, nuances in legal precedent also present an issue. Often, a "taking" in 5th Amendment terms is not a full taking, and thus, the government is not required to compensate property owners for their loss in value. In the legal profession, this is usually known as a "regulatory taking"; where the legislature or a executive agency passes new law or regulation that forbids a certain kind of use on a piece of property, rendering it useless to the property owner.
This is not necessarily the standard now. A recent United State Supreme Court case from 2012 held that a temporary taking, not a full or outright dispossession of property, would require the government to compensate private property owners for their loss of value to their land or property.
This case could have huge implications for the pending litigation surrounding the flooding of the Barker and Addicks reservoirs. The United States Army Corp of Engineers consciously knew that certain homes would likely be flooded if they opened the reservoirs, rendering those houses that flooded unlivable. The "taking" by the flood waters was temporary, given that the flood waters have receded. As such, according to Supreme Court legal precedent, this would force the Army Corp of Engineers and other entities that a court finds liable, to compensate people that had their houses flooded as a direct result of the opening of the reservoirs.
Historically, there is a requirement that taking must be permanent, but that could change with pending litigation.