Final answer:
The government must offer just compensation to Frank for condemning his property, according to the Takings Clause of the Fifth Amendment, which permits eminent domain provided the property is taken for public use.
Step-by-step explanation:
When the government sends a notice that a property will be condemned, as in Frank's situation for a water treatment plant, the government is required to offer just compensation in exchange for his property. This requirement is rooted in the Fifth Amendment to the United States Constitution under the 'Takings Clause,' which ensures that private property cannot be taken for public use without such compensation. The terms 'public use' and 'just compensation' are not specifically defined in the Fifth Amendment; however, the courts have historically upheld the government's eminent domain power. In essence, this allows the government to take private property to serve the public good, provided that they pay a fair price for it.