The type of water tank my aunt has on her property

My aunt Maggie retired last year and was happy to do so. My aunt Maggie had been a busy business consultant for the past fifteen years. She ran her own business and was very good at what she did. She was running her business in downtown San Francisco. When she retired she moved to a small coastal mountain range in central California. She wound up with a nice little ranch home with twenty seven acres of pasture. Within a year she had brought in a rain water tank and was running four horses on her property. I like going to visit her.