הלכות רוצח ושמירת הנפש

It is a positive commandment for a man to build a guardrail for his roof, as Deuteronomy 22:8 says: "And you shall make a guardrail for your roof."
This applies with regard to a building used as a dwelling. But for a warehouse or a cattle barn and the like, there is no necessity. Similarly, any building that is not four cubits by four cubits does not require a guardrail.

A house owned by two partners requires a guardrail. As can be inferred from Deuteronomy 22:8: "For one who falls may certainly fall from it," the obligation stems from the fact that one may fall.
If so, why does the verse state "your roof"? To exclude synagogues and houses of study, for they are not intended to serve as dwellings.
If the public domain is higher than a person's roof, he does not need to erect a guardrail, for the phrase "For one who falls may certainly fall from it" implies that the guardrail is intended to prevent people from falling "from the roof," and not onto the roof.

The height of a guardrail should not be any less than ten handbreadths, so that a person who might fall will not fall from it.
A guardrail must be a partition strong enough to enable a person to lean on it without falling.
Anyone who leaves his roof open without a guardrail negates the observance of a positive commandment and violates a negative commandment, as Deuteronomy 22:8 states: "Do not cause blood to be spilled in your home." The violation of this commandment is not punished by lashes, for it does not involve a deed.

This requirement applies to a roof, and similarly, to any place that might present a danger and cause a person to stumble and die. For example, if a person has a well or a cistern in his courtyard, he must erect a sand wall ten handbreadths high around them or make a cover for them, so that a person will not fall in and die.
Similarly, it is a positive mitzvah to remove any obstacle that could pose a danger to life, and to be very careful regarding these matters, as Deuteronomy 4:9 states: "Beware for yourself; and guard your soul." If a person leaves a dangerous obstacle and does not remove it, he negates the observance of a positive commandment, and violates the negative commandment: "Do not cause blood to be spilled."

Our Sages forbade many matters because they involve a threat to life. Whenever a person transgresses these guidelines, saying: "I will risk my life, what does this matter to others," or "I am not careful about these things," he should be punished by stripes for rebelliousness.

They include: A person should not place his mouth over a conduit through which water flows and drink. Nor should he drink at night from rivers and lakes, lest he swallow a leech without seeing.
Similarly, a person should not drink water that was left uncovered, lest a snake or other poisonous crawling animal might have drunk from them, and as a result, the person would die.

These are the liquids that are forbidden if left uncovered: water, wine - even watered-down wine, or wine whose flavor has begun to change to vinegar - milk, honey, and brine. Other liquids are not forbidden if left uncovered, because venomous animals will not drink from them.

When garlic has been crushed or a watermelon cut open and left uncovered, they are forbidden. The same applies in all analogous situations.
The prohibition against drinking uncovered beverages does not apply to wine that has been boiled or to unfermented wine. Unfermented wine refers to wine from the time it was squeezed from the grapes until three days have passed.
Similarly, the prohibition against drinking uncovered beverages does not apply to wine, water or milk that are hot to the extent that vapor arises from them, nor to liquids into which liquid is descending from above drop after drop, providing the liquid continuously descends. For crawling animals fear bubbles and vapor, and will not drink from them.

The prohibition against drinking uncovered beverages does not apply to water used for pickling, cooking food or cooking vetch. Similarly, this prohibition does not apply when pickled foods, cooked foods or vetch have been left to soak in water, if they have changed the taste of the water. If they did not change the taste, the water is forbidden if left uncovered. Similarly, water in which quince and Syrian pears were washed for a sick person is forbidden if left uncovered.

The prohibition against drinking uncovered beverages does not apply when sharp tasting substances like pepper, or bitter substances like wormwood are mixed with wine to the extent that its flavor changes. The same applies with regard to other beverages.

When a liquid is forbidden if left uncovered, it is forbidden whether it was left uncovered during the day or during the night. This applies even when a person was sleeping beside the liquid. For crawling animals are not afraid of sleeping men.
For how long must a liquid be left uncovered to be forbidden? For as long as it takes for a crawling animal to emerge from under the container, drink, and return to its place.

The quantity of water that becomes forbidden if uncovered is an amount in which the venom could remain a distinct entity and cause danger. If, however, there is so much that the venom will be nullified as if it does not exist, the water is permitted. This applies to water contained in utensils or on the ground. The same law applies to other liquids.

The prohibition against drinking uncovered beverages does not apply to a stream that is flowing, even slightly.
When a container of wine is left uncovered in a chest, a bureau or a closet, or in a larger container in a pit that is even 100 cubits deep, in a tower that is 100 cubits high, or in a hall that is ornamented and plastered, it is forbidden.
If the person checked the bureau or the chest and then put the wine there, it is permitted. If there was a hole in the chest, it is forbidden. How large must the hole be? Large enough for a child to insert his small finger.

When a jug is left uncovered, a person should not drink from it, although nine people drank from it before him without dying.
An incident occurred, and it was reported that the tenth person who drank from a jug died, because the venom of the snake sank to the bottom of the jug. And there is venom from some crawling animals that rises to the surface of liquids, and other venom that becomes suspended in the middle. Therefore, everything is forbidden. This applies even if one filtered the liquid with a filter.
Similarly, when a watermelon was left uncovered, even if nine people partook of it without dying, a tenth should not partake of it.

Water that was left uncovered should not be poured into the public domain, nor should it be used to settle the dust of a home, nor should it be used to mix mortar, nor should it be used to wash one's face, to water one's animal or an animal belonging to a colleague. It may, however, be used to water a cat.