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Worms — Part III: Permitted Worms


Continuing our series of articles on the laws of worms, this week we will address the question of which worms the Torah permits to consume. Are tiny worms like zooplankton, which are commonly found in bodies of water, permissible? Is there an issue with drinking tap water in New York City, given its purity and potential for containing such organisms? What about water from the Kinneret? How does the halacha apply to Israeli cities that draw water from the Kinneret?

Additionally, we will discuss whether there is a difference between drinking directly from a reservoir or water cistern, versus from a cup. When should one exercise caution to avoid swallowing water from a reservoir while swimming, and when is it not a problem? We will also address the laws pertaining to situations where one finds the presence of worms in water repulsive, or if there is a health risk involved.

Wormy Reservoir Water

Some reservoirs contain tiny worms, and while without careful examination, the water appears clean, it might actually be infested with tiny worms. Even in developed countries people drink from these reservoirs. One such example is New York City, and the question arises: is drinking this water permissible? Can a traveler drink water from a river or a random spring?

The Gemara (Chulin 66b, 67a) learns from psukim that it is prohibited to consume water insects formed in seas and rivers. Moreover, there are situations where there is more than one prohibition involved (Eruvin 28a, Pesachim 24b, Makkos 16a). However, insects formed in stored water, or in wells, pits, and caves, are permitted for consumption. This permission is subject to many restrictions which we will address later. Therefore, it is permissible to drink directly from the vessel or reservoir, even if it contains small worms.

In addition, there is a place which the Gemara calls ‘Charitzin and Neitzin,’ in which there is a dispute among the Tannaim whether creatures that formed there are permissible. There is a dispute among the Rishonim regarding what ‘Charitzin and Neitzin’ are, and another dispute: how the halacha was settled.

The halacha is decided (YD 84:1) that water that collects in a reservoir without a natural spring, and without an outlet, such as a puddle or cistern is considered like a utensil, and creatures that form there are permissible for consumption. However, where the water has an outlet, the Shulchan Aruch (YD 84:1) notes a dispute concerning its creatures’ status. In practice, the Shach (YD 84:8), Ohr Hachayim (Pri Toar 84:4), Chida (Machzik Bracha YD 84:2), Pri Megadim (YD 84:8), Zevchei Tzedek (84:13), and Kaf Hachayim (YD 84:17) write that one should be stringent. However, the Pri Chadash (YD 84:7) is lenient. The Pischei Teshuvah (YD 84:1) cites the Mishkenos Yaakov (YD 29) who writes that according to the basic law, the halacha follows the lenient opinion of Rosh, but in practice, one should be stringent. Mainstream halacha is stringent here, but where there are additional reasons to be lenient, a rabbi might adopt the lenient approach.

Natural Habitat

When a creature leaves its natural habitat, even if it only ventures to a nearby location—such as moving from the water in a cistern to its outer edge or rim—and then returns – it renders the water forbidden for consumption. Drinking this water is prohibited unless it undergoes proper filtration.

However, if the creature remains within the vessel or well, even if it climbs onto the inner edge of a cup or the inner lip of the well and then returns to the water, the water remains permissible for consumption. This is because the entire vessel or cistern are considered the natural habitat, and the creature has not truly left it.

Additionally, according to the Shulchan Aruch (YD 84:1), if there is no clear evidence that the worms have exited the water, there is no need to be concerned that they might have left and returned.

Drinking From a Cup

The Rema (YD 84:1) ruled that infested water drawn from a reservoir to another vessel is forbidden because there is concern that a worm might have emerged from the water and returned, as they commonly do. Therefore, drawing water to drink in a cup is forbidden.

The Shach (YD 84:5) adds that it is also forbidden to drink water in one’s hand. The only permissible method to consume infested water is to drink directly from the reservoir or cistern.

On the other hand, the Rema (YD 84:3) permits transferring infested water from one vessel to another, provided that the worm moves with the water. How is an infested vessel different from a cistern or well? There are three approaches to understanding this distinction:

The Shach’s Approach

The Shach (YD 84:4) explains that if worms form inside a vessel, the entire vessel, including its inner sides (outside the water), is considered its habitat. If the water was poured from one vessel to another it remains permitted, even if the worms jump in and out of the water inside the second vessel, since the natural habitat is a vessel. However, worms that were formed in a pool or cistern, once drawn into a cup, are no longer considered in their natural habitat, and we are concerned they might jump out of the water and become prohibited, even if they remain inside the perimeter of the cup. Even if there is no definitive evidence that the worms left the water and returned, we are concerned it may have happened (because that is what the worms normally do). This approach is supported by many poskim.

The Ohr Hachayim’s Approach

The Ohr Hachayim’s approach (Pri Toar YD 84:1) is that if the worm was formed in a water reservoir as a result of the earth’s moisture, its natural habitat is only the reservoir, not a vessel — while for a creature that formed in a vessel, its natural habitat is only in the container. Therefore, even though the creature moved from the water reservoir to the vessel inside the water, the creature is no longer in its natural habitat and is forbidden for consumption. This is also the opinion of the Zivchei Tzedek (84:1) and the Kaf Hachayim (YD 84:10).

The Taz’s Approach

The Taz (YD 84:5) argues that if there is already water in a cup before more water is added, there is no concern. However, if water is drawn into an empty container, we are concerned that a worm may have entered first without water, rendering the rest of the water forbidden.

The Pleisi (YD 84:1) elaborates on the Taz’s approach, explaining that the distinction is not between a cistern and a vessel but rather in how the water is transferred between them. When water is poured from one vessel to another, it remains permissible. However, if a bucket is dipped into a well or cistern, there is a concern that worms on the lip of the vessel might fall back into the water, thereby rendering it forbidden.

Drinking Unfiltered Water from a Large Reservoir

This ruling raises an important question: Is it permissible to drink water from a large reservoir that is not fed by a natural spring, which the local municipality pipes into the local water system?

Rav Vozner (Shevet Halevi, Volume 7, Chapter 123) explains that the answer depends on the aforementioned rulings:

According to the Taz and Pleti if the water flows immediately into the pipeline as soon as the faucet is turned on, and no worm has a chance to enter the pipelines before the water, drinking the water is permissible.

According to the Shach’s approach if there is a section of the pipe where worms can exit and re-enter the water, such as if the water does not fill the entire pipeline, using the water without filtering is forbidden, due to the concern that worms have exited and returned to the pipeline. However, if the pipe system is constructed so that it is entirely filled with water, leaving no space without water, only drinking directly from the pipeline is permitted.

According to the Ohr HaChaim’s approach, drinking the water is impossible, as the mere fact that it moved from the reservoir to the pipeline is enough to prohibit it.

Note: This ruling does not apply to New York City’s water system because the water there also originates from natural springs, as will be detailed further.

Practical Ruling:

According to Rav Vozner, one should be stringent and follow the Ohr HaChaim’s approach, but retrospectively, there is room to be lenient according to the Shach’s approach.

Additional Restriction Based on Worm Species

Another restriction on this ruling depends on the species of the worms. According to the Chazon Ish (YD 14:10), if a creature reproduces from a male and female, and the male originates from elsewhere but reproduces in the water, consuming it is forbidden even though the creature was born in the water and never left it.

Winged Creatures

The poskim (Knesset HaGedolah YD 84, glosses on the Beis Yosef 3; Pri Megadim YD 84:10; Chochmas Adam 38:4; Zivchei Tzedek 84:17; Kaf HaChayim YD 84:23) clarify that the permission to consume water creatures is limited to those that cannot fly. Any creature that has wings or fins, and is capable of flying or swimming in water is forbidden for consumption.

Detestable Things

The Taz (YD 84:2) introduces another restriction: drinking infested water is only permitted when the water is not considered detestable. For instance, millions of New York City residents enjoy their drinking water despite the presence of zooplankton worms in the water. However, for a sensitive individual who is disgusted by the worms or by the knowledge of their existence in the water, consuming it would violate the prohibition against engaging in repulsive activities (YD 116:6). Even if such a person is thirsty and wishes to overcome his disgust, it remains forbidden. This prohibition is especially relevant in less developed areas where even an ordinary person finds the water repulsive.

Health Hazard

The Taz (YD 84:2) emphasizes that if consuming water containing worms poses a health risk, as is often the case in developing countries, it is strictly forbidden to drink the water. This prohibition applies even in situations where the worms would otherwise be permissible.


Drinking water from a closed, non-spring-fed reservoir that contains worms is permissible only if one drinks directly from the reservoir, such as while swimming in it. This is conditional upon the worms being neither detestable nor harmful to one’s health.

Water that has been stored in a covered vessel that has become infested is permissible to drink if the worms are not considered detestable, such as tiny worms that people typically do not mind.

In all other scenarios, it is advisable to filter the water through cloth before drinking. In many cases, this step is mandatory to ensure the water is safe and free from contaminants.

Eating a Worm

The Pri Chadash (YD 84:6) states that if a worm exits the water but remains on the inner surface of the vessel or cistern, it is still considered within its natural environment and is thus permitted for consumption. However, consuming the worm by itself, even if it is still within the cistern, is prohibited. The Pri Megadim (YD 84:4) adds that while the worm is not prohibited when out of the water, it becomes immediately prohibited if it enters the mouth without water.

Infested Liquids

These laws extend to any liquids that contain worms, not just water. Authorities such as the Shach (YD 84:1), Pri Chadash, Pri Megadim (YD 84:1), Kereti, Chochmas Adam (Klal 38:2), Zivchei Tzedek (YD 84:1), and Kaf HaChayim all agree. Rabbi Yehoshua Mikutna (Yavin Daas), cited by the Shevat HaLevi (Volume VI, Chapter 123:1), rules that the leniencies cited above apply only to those liquids that halacha defines as liquids (i.e., dew, water, wine, olive oil, blood, milk, and honey). This permission does not extend to other liquids, with the exception of date beer, as its main ingredient is water boiled with dates. Thus, infested fruit juice or apple cider vinegar would be prohibited. However, this stringent opinion is not widely accepted and need not be considered, as most poskim disagree.

Mixing Infested Vinegar

A question arises regarding the permissibility of using vinegar containing small visible worms in cooking or salads. The issue is whether the worm is considered separated from the vinegar and thus prohibited when mixed with other foods.

This topic is debated by many poskim:

The Shach (YD 84:10) writes that if infested vinegar is mixed into a dish, it is still considered within its natural environment, and consuming it remains permitted. The Pri Chadash (YD 84:9) concurs but notes that if the worm moves from the dish to the inner side of the container, it becomes prohibited, despite the general rule that the entire interior space is the worm’s natural surroundings. Therefore, pouring vinegar into a boiling pot, where the worms immediately die, is permitted. However, for cold salads, one must ensure the worms do not leave the food, and the dish should be eaten during the day or under strong artificial light.

The Pri Toar (YD 84:6) maintains that this permission applies only to liquids, and once the worm passes into the solid part of the dish, it is no longer in its natural environment, and is thus prohibited. The Pri Megadim (YD 84:5) was uncertain but leans towards permitting it, though he practically suggests being stringent.

The Chazon Ish (YD 14:3) agrees with the Pri Megadim, allowing it when the liquid exceeds the food. Additionally, if the worm is on a fish in the water, it is not considered separated.

The Pri Chadash (YD 84:33) and Pri Megadim (YD 84:8) rule that bread baked with wormy water is prohibited, as the kneading process moves the worms from their natural habitat.

New York City’s Water

An interesting problem emerged in New York City, renowned for its pure and clean water. The issue arose following an intriguing incident: a G-d fearing Jew purchased high-quality kosher lettuce, washed it thoroughly, and inspected it in sunlight for worms. To his surprise, he discovered tiny worms on the leaves. Despite repeatedly washing them, the worms persisted. He tried another package with the same result.

The concerned individual contacted the company, which took the complaint seriously and urgently requested a sample. After examining the sample, the company responded that the creatures were zooplankton, a family of mostly microscopic life forms, some of which are visible to the naked eye. These zooplankton were present in the water, not originating from the lettuce itself. They verified this by checking dry lettuce – there were no worms in the lettuce. However when the tap water was inspected, it revealed many of these creatures.

According to the municipality, because New York City’s water is purer and cleaner than most places, there is no need to filter it, leaving the zooplankton intact. This contrasts with most other locations in the US and Western world, where water filtration is standard practice. The city does treat the water, though, so the zooplankton are no longer alive, but they do, nevertheless, remain whole.

To check for the presence of zooplankton in the water, one should place a double layer of white cloth over the tap for several days. Then, the cloth is removed and examined carefully for worms. A magnifying glass can be used initially, and if worms are found, one should try to determine if they are visible without magnification.

This issue has sparked a wide-ranging debate among the poskim, and individuals are advised to consult their LOR. Those who prohibit the water argue based on the issues discussed in this week’s article: although the zooplankton in New York City’s water system are no longer alive due to treatment, their legs and antennae are still visible upon careful inspection. When alive, their movement is noticeable enough to prohibit them. Additionally, some of the city’s water sources are spring waters, which could contribute to infestation.

Kinneret Water

The Kinneret supplies 20% of Israel’s drinking water and is known to be infested with zooplankton. However, tests conducted by Rabbi Moshe Vaya across many Israeli cities indicate that the filtration process and various treatments ensure no whole worms visible to the naked eye remain in the drinking water, even in cities that consume Kinneret water.

For example, several years ago, the Israeli Ministry of Health reported that Tel Aviv’s drinking water contained a type of mosquito. Although there was no health concern, the halachic issue remained unresolved. To the best of our knowledge, this problem was quickly addressed, but similar issues can potentially recur in any water reservoir.

It is important for individuals to stay informed and cautious regarding the quality of their drinking water, ensuring it meets both health and halachic standards.

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