Shabbat 14 - The Eighteen wins of Beit Shammai
The eighteen decrees of Beit Shammai, which they were able to promulgate forcefully, outnumbering Beit Hillel, concern mostly with matters of ritual purity, which are only important in the times of the Temple and in dealing with ritually pure foods. However, some of them have ramifications even today, when there is no Temple. Below are three of the eighteen.
One whose head and body enters drawn water (such as tap water or water brought in a pail) becomes ritually impure. That sounds upside-down: water makes impure. However, the reason for this is that people who did not have a proper clean mikveh to purify themselves used to immerse in a dirty stale water, naturally assembled in caves. While being a ritually valid mikveh, it would make one physically dirty, and he would then take a shower. Eventually, people starting thinking that the shower has the power to ritually purify a person, which was not true. There, if one cannot use the shower without loosing the effect of his prior immersion in a mikveh, this practice stops and the confusion is eliminated.
One who was not paying attention to his hands after he washed them last the time, being it for prayer or in the morning (pouring water on them alternatively three times) should assume that he has touched something ritually impure, and now he has to wash them again, before he touches a pure food, or before he prays.
If one who touches a Torah scroll with his hands, they becomes ritually impure. That seems counter-intuitive, but the reason is that people used to store the Torah scrolls and ritually pure foods together, thinking they both are holy. However, mice would find the food and would also eat the scroll. With this decree, people would not store them together any longer.
Art: Joos De Momper - A Mountainous Landscape With Travellers And A Hermit Outside A Cave With A Waterfall