Rainwater collection is one of the oldest means that humans have of getting water. While it has seen a resurgence in popularity as a way to combat drought while protecting water supplies, there are also some areas where laws are specifically in place to stop people from collecting rainwater that falls on their property.
Some places in the country, rainwater collection is not only illegal, but has been so for a long time, says Popular Mechanics. In the state of Colorado, for instance, the rainwater that falls on a person's property does not in fact belong to the homeowner. The state has a rigidly regimented water allocation system, especially in areas like Denver. If one person captures rain it wouldn't make much of a difference but if a large portion of a city does it then it can throw off the whole system.
While rainwater collection may be illegal in places like Colorado and Utah, there are states like Washington where it's as common as the rain itself. A caveat that states rainwater collection can be outlawed or altered based on local laws is common in such states. When the discussion comes up about making rainwater collection illegal, the local government has a responsibility to alter the laws to protect the environment if it can be shown that homeowner collection of rainwater is damaging the municipal groundwater supplies.
Some types of use and storage for rainwater require a permit. For instance, if a homeowner is going to collect rainwater and store it underground for use in the springtime then that person has to get a permit from the local government establishing that the storage tank is legal and allowed (in Washington State at least). Rainwater can be drunk if it's purified but most homeowners use it for gardening and lawn growing purposes.