With all the recent rains hitting the state of Texas is it possible, and legal, to save that rainwater? In some states it is actually not illegal to save and store rainwater for later use such as watering plants/crops or for animals to drink but is heavily restricted. The answer is why would something that's natural be restricted?
Some of those other states don't allow the storing and saving of rainwater for potential future use because of bacteria, possible pollutants and even the way it's stored which is a big factor. The way the water is stored can be in giant containers that have to have some type of plumbing done which will have to follow certain laws since they would have to follow certain laws.
In the state of Texas it is not illegal or restricted to collect rainwater but is actually encouraged and incentivized according to the Texas Water Development Board website. Texas also has laws that support rainwater harvesting due to it reducing the demand of traditional water supplies along with it being free.
If you decide you want to start collecting rainwater then it is possible to gain an exemption, partial or full, on those harvesting units property values. The Texas Tax Code also exempts equipment, supplies and labor from state sales tax but before you get to building you might do some research. It's advised to check with your county and local water providers to check their water conservation initiatives and how your harvesting system would be included.
Of course you can't collect rainwater in Texas without making it some sort of a competition. There is a Texas Rain Catcher Award which is used to promote rainwater harvesting in the state among individual people, organizations and municipalities. The application for that award must be submitted by June 30 every year. A more detailed information about rainwater collecting in Texas can be found online.