1. It is forbidden for men (starting at Bar Mitzvah) and women (starting at Bat Mitzvah) to eat or drink anything on the seventeenth of Tammuz. The fast begins at dawn (amud ha’shahar) and ends at Tzait Ha’Kochavim — when the stars come out, approximately 40-45 minutes after sunset.

2. Although we are permitted to eat and drink the entire night before, once a person falls asleep, his fast begins immediately because we assume that he has no intention to eat or drink thereafter. This applies whether it is “regular” sleep (even if it is not in bed) or a nap (even during the meal).

a. If he is coherent during his nap, i.e. if when reminded where he placed something, he can answer immediately, then he is still permitted to eat and drink. 

b. If one slept before the evening meal eating is still permitted.

c. If one makes a condition before he goes to sleep saying that he wants to eat and drink when he wakes up, then he is permitted to do so.

3. Washing is permitted on the seventeenth of Tammuz. One may even wash one’s entire body with hot water (ובעל נפש יחמיר).

4. a. It is appropriate to be strict and not rinse one’s mouth on this fast day, because we are concerned that perhaps he will swallow the water.

b. Nevertheless, if he is accustomed to rinsing his mouth, and not doing so will be difficult for him, he may do so. However, extra care must be taken not to swallow even the slightest amount of water. One should also be careful not to rinse with more than a rivi’it (three ounces) of water.

c. The same law applies to brushing teeth.

5. a. It is permissible to taste a food or drink (by placing it on the tongue) to determine if it needs more salt or spice. One must be sure not to taste more than a rivi’it (three ounces) and it should not be swallowed.

b. It is permitted to taste the food for this purpose even several times during the day.

6. a. An otherwise healthy person who suffers from a headache during the fast is permitted to take medicine to relieve it as long as it is not flavored and he swallows it without water.

b. If a person is sick or has a condition that requires daily medication he is permitted to take it, even if it has flavor if it cannot be substituted with an unflavored kind.

7. a. Even if a person accidentally ate and drank on the seventeenth of Tammuz, he should still fast for the remainder of the day.

b. One is not required to fast on another day to make up this fast.

c. If one ate more than a kezayit (one ounce) it is questionable whether or not he may recite Aneinu (the special prayer recited on fast days during Shemoneh Esrei) during the Prayer Service.

8. If he accidentally forgot that it was a fast day and made a blessing over a food, he should eat a tiny amount so as not to have recited the blessing in vain.

9. It is not permitted to chew gum on a fast day because the flavor is swallowed.