Before you purchase any property with a cistern, you should contact the local water district and/or your local municipality and ask this question. There are some companies that will deliver water to you, but it's not always the most economical way to get your water. You might want to get a truck or trailer, with a cistern mounted in it, and get your own water. Some municipalities have had free (or extremely inexpensive) water if you were able to pick it up.
It might make sense to drill a well, as the cost of water over a 5 year period might end up being higher than if you drilled a well now.
Best of luck, and please know that these are questions that your REALTOR Buyer's Agent can help you find answers for, as well.