Probably because it happened before your birth, perhaps even before the birth of your Great Grandparents.
By the way, and the following is true: I have even showered in a situation where I hauled 5 gallons of water to the shower, filled the container and showered during the time that it took for the water to run out and when it did, my shower had ended. But, that was O.K. I was glad to be able to shower once a week. I knew that I could have another shower in a week.