Those who are Exempt from Fasting
All adults are obligated to fast on a Ta'anis Tzibbur, and one may not divert from this enactment.
Children until the age of Bar (or Bas) Mitzvah are exempt from fasting. They are not required to delay their regular eating schedules at all.
A person who is sick can eat as usual, even if fasting would not endanger his life. He is not required to eat small amounts in intervals (as on Yom Kippur) since the fast was not enacted by Chazal for sick people. He may not decide to act stringently in the matter.
The definition of a Choleh (a sick person) regarding these Halachos is as follows: One who would be allowed to take medication on Shabbos - namely, someone who is bedridden or weak and unable to function normally.
Someone who can function as usual, even though he is suffering from a mild pain or discomfort, is still required to fast.
Pregnant women are exempt from fasting - from when they know that they are pregnant, even within the first 40 days of conception.
Similarly, nursing women are exempt from fasting, even if the child is also receiving supplementary food. However, if she has completely stopped nursing, she is required to fast, even if she is still within 24 months of giving birth.
A woman who gave birth within 30 days of the fast-day does not fast, regardless of whether she is nursing or not. One may be lenient to calculate the 30 days from the time she gave birth (not from the beginning of the day she gave birth).
After a miscarriage (after forty days), she has the status of a postpartum woman and is exempt from fasting.
Someone who is obligated to fast is expected to take precautions to ensure that he is indeed able to do so. Therefore, if due to exertion he will become weak and will not be able to fast, he must rest during the day of the fast in order to successfully complete the fast.
Even those exempt from fasting, as above, should not indulge; They should not eat meat, drink wine, or enjoy luxuries.
Children who do not understand the concept of mourning, are not restricted in what they may eat and drink.
Conduct for the Night of the Fast
The Evening Before the Fast
The fast begins at dawn (Alos HaShachar) and ends at nightfall.
The two main opinions as to when is Alos HaShachar are: a) 90 minutes before Netz HaChamah; b) 72 minutes before Netz HaChamah. One may be lenient and eat until the later of the two above-mentioned times.
Although the Poskim mention that a meticulous person (Ba’al Nefesh) should refrain from eating already on the eve of the fast (as is incumbent on Tishah B’Av and Yom Kippur, see below), nevertheless the custom is not to be particular in the matter and even a Ba’al Nefesh can eat until Alos HaShachar.
Strictly speaking, one may eat meat and drink wine on the eve of the fast, however some are stringent in the matter (עי' סי' תק"נ, תוה"ש יו"ד סי' קפ"ה סק"י, סדה"י ענין י"ז בתמוז) .
One should refrain from joyous get-togethers on the eve of the fast, unless they are some form of Seudos Mitzvah (e.g. Bris Milah, Pidyon HaBen, Siyum) that are set to take place at that time. A Chasuna may be held on the night of the fast (עי' תוס' עירובין מ: ד"ה דלמא, ושו"ע סי' תק"נ ס"נ) . Even so, it is best to avoid Sheva Brachos celebrations that are unnecessary.
Sleep as Acceptance of the Fast
Although the fast begins at Alos HaShachar (dawn) as above, nevertheless a proper sleep at night (שינת קבע) is considered as actual acceptance of the fast. Therefore, if a person wakes up in the middle of the night, he may not eat thereafter. However, a short nap is not considered as an acceptance of the fast, and if one wakes up from such a nap before dawn, one may still eat and drink.
If one made a stipulation before sleeping that he plans to eat after waking up, it is permitted for him to eat until Alos HaShachar. However, according to Kabbalah (the Zohar), one should refrain from eating after waking up in the middle of the night (after Chatzos), even on regular nights. Still, if abstaining from food would make it difficult for a person to fast or prevent him from studying Torah properly, he may eat - in accordance with the basic Halacha - until dawn. Drinking is permitted even according to the Zohar.
If one usually sleeps at the beginning of the night and then wakes up and eats, that initial sleep is not considered acceptance of the fast, and it is permitted to eat after waking up.
If one dozed off or even had a proper sleep in the middle of his evening meal, he is allowed to resume eating upon waking up. (However, one who chooses to be stringent in this regard is praiseworthy.)
Drinking after sleeping on the night of the fast: One may drink all beverages, even if he did not make a stipulation before going to sleep. However, ideally, one should make such a stipulation beforehand. For Bnei Sepharad, who follow the opinion of the Shulchan Aruch, it is prohibited to drink after sleeping unless a stipulation was made in advance.
In all cases where one may eat or drink after awakening before Alos, there are no limitations regarding the amount of food or drink that he may consume. (This differs from a regular day where within a half hour before Alos one may not begin to eat more than a Kebeitzah of bread or Mezonos).
Halachos of the Ta’anis
Rinsing out the Mouth
One should not rinse out one’s mouth. If this causes great discomfort and is very disturbing to him, he may do so. He must tilt his head forward to ensure that he will not come to accidently swallow any water.
Brushing Teeth
Since the mouth is rinsed after brushing one’s teeth, one should refrain from brushing one's teeth on the day of the fast. If this will cause great discomfort or is a question of human dignity, one can be lenient as above.
Taking Medication
If someone fasting is required to swallow a pill, he may do so, preferably without water.
If he must drink some water to help him swallow it, he should add some bitter flavor, e.g. salt or bitter tea essence. The same should be done prior to taking a medication that has a sweet taste (as with some syrups).
Smoking
One may not smoke electric cigarettes on the day of the fast. Regular cigarettes are permitted for a person who finds it very difficult without, but only in private. (Keep in mind - even throughout the entire year smoking is detrimental to one’s health and to the health of those around him).
Music
One should refrain from listening to music on a fast-day (קיצור שו"ע סי' קכ"ב, וע"ע סי' תקס"ח סע' י"ב). This is so already from the eve of the fast. (עי' משנ"ב סי' תק"נ סק"ו, וע"ע בא"ח שנה א' פרשת דברים אות ה')
Bathing
On the night preceding a fast day: According to the strict Halachah, it is permitted to wash in hot water as usual. (Below it will be explained that a Ba'al Nefesh is stringent not to wash at all, even in cold water, and even on the night before the fast.)
On the fast day itself: Sephardim may wash with hot water as usual. Ashkenazim should refrain from washing the entire body in hot water (שע"צ סי' תק"נ סק"ח) , but it is permitted to wash one’s face, hands, and feet with hot water. However, if the water is not hot enough to derive pleasure from its warmth, one may wash even the entire body. (It will be explained that a Ba'al Nefesh is stringent not to wash at all, even with cold water, see #31.)
Laundry, Haircuts and Shaving
Strictly speaking it is permitted to launder clothes, to take a haircut, and to shave on a fast-day
One who Ate During the Fast
If someone forgot and ate or drank during the fast, regardless of the amount, he must abstain from further eating and must fast until the end of the day. He is not required to make up the fast on a different day. He should invest time and effort to study properly the laws of a fast and thereby in some way atone for the mishap.
Reciting Anenu
Regarding saying “Anenu” in the Shemoneh Esrei – if he ate less than a Kezayis or drank less than a cheek-full (Meloy Lugmav), he still adds Anenu.
However, if he ate more than a Kezayis [some say more than a "Koseves" – the size of a date] or drank more than a Meloy Lugmav, he can no longer say in Anenu the words ביום צום תעניתנו, rather he says ביום צום התענית הזה.
A Choleh who is required to eat does not say Anenu. The same applies to a minor who is not fasting.
Applying Dinei Tishah B'Av to the Other Fast Days
The Mishnah Berurah cites opinions that even on the lenient fast-days (17th of Tamuz, Tzom Gedalyah, Asarah BeTeves, Ta'anis Ester), a meticulous individual (Ba’al Nefesh) should observe the same restrictions as on Tishah B’Av. This includes refraining from bathing or showering - even with cold water - from the eve of the fast. Likewise, he should avoid applying ointments or creams (however, in a case of medical need, a Rav should be consulted).
Regarding eating on the eve of the fast – even a Ba’al Nefesh is not required to be stringent.
A Ba’al Nefesh should refrain from marital relations on the night before the fast (unless it is the night of his wife's immersion).
Regarding wearing leather shoes, a Ba’al Nefesh should not adopt stringencies in public, as this may be perceived as arrogant behavior or draw ridicule. However, in the privacy of his home, he may choose to be stringent - starting from the eve of the fast - and refrain from wearing leather shoes, as on Tishah B’Av.
After the Fast
Meat and Wine
After the fast has concluded, also a Ba’al Nefesh may eat meat and drink wine. (סי' תקנ"ח סק"ה, ועי' סי' של"ד ס"ק ע"ט) .
Eating Before Maariv
After the fast ends, it is permitted to eat even before Maariv. However, since the Heter of relying on davening with his “fixed Minyan” later in the evening (which on a regular day would allow him to eat supper before Maariv) does not apply here, because in most places there is no fixed Minyan for Maariv immediately at the end of the fast. Therefore, one must be careful not to eat before Maariv more than a Kebeitzah of bread or Mezonos, and likewise not to drink alcoholic beverages in an amount greater than a Kebeitzah. Other foods, however, may be eaten even in large quantities.
If one wishes to eat more than a Kebeitzah of bread or cakes, he must appoint a Shomer (a guard) who is not eating, or he must set an alarm clock and display on the screen “Krias Shema and Maariv”.