We often post about harvesting rainwater as an off-the-grid water solution. This will allow the owner to use rainwater around a homestead, which is drinkable, for irrigation, watering livestock, and inside the home for washing and even drinking if needed. Although it might be a good prepping device, needless to say, if the air is chemically polluted, rainwater will get polluted as well.
However, as weird as it sounds, this is illegal in some states, and there are regulations for it in others. So, if you are planning on harvesting rainwater please check the link below to see the legislation in your state.