Tap water may not be safe depending on where you drink it. Although the tap water itself is clean, many local water tanks are not maintained properly, and one should try to avoid tap water if possible. Locals widely prefer bottled water and the same applies for the restaurants. Expect to pay for water in restaurants around 2TL.
Food and drinks are mostly of international standards. Some Turkish foods are known to use a variety of spices which may affect international tourists who may not be accustomed to such ingredients, although most of it is edible for any tongue.
Use common sense when buying certain foods, particularly from street vendors. Delicacies such as "Firin Sutlac" a kind of rice pudding can go bad rapidly on a hot day, as can the oysters occasionally for sale on the streets.
As with most European cities, but especially in crowded areas of Istanbul, watch your pockets and travel documents as pickpockets have devised all sorts of strategies to obtain them from you. Do not rely too much on the 'safe' feeling you get from the omnipresence of policemen.
Istanbul is home to three of the biggest clubs in Turkey and arguably European football: Beşiktaş, Fenerbahçe, and Galatasaray. It is advisable not to wear colours associating yourself with any of the clubs—black&white, blue&yellow, and red&yellow respectively, particularly on the days of matches between the sides due to the fearsome rivalry they share.
internet
Cafés with free wireless internet wi-fi:
Several of the nargile places in Tophane
Several cafes in Cihangir, including Kahvedan, Meyva, Komşufırın and Kahve Altı
Many cafés and restaurants along Istiklal Caddesi in Beyoglu
Both the large American fast food restaurant chains
There is one upstairs by the restaurants facing the side of Aya Sofia and behind the entrance to the Basilica in Sultanahmet.
Starbucks has quite a few shops around, and at least those at the touristic zones, has a free wireless connection.
In the recent years, the number of cafes and shopping centers with wi fi Internet access has increased dramatically, most of them still being free. Most internet cafes have high speed ADSL connections, and they are very inexpensive compared to Europe about 0.50-1.50 Euros per hour.
Most hostels and hotels of the Sultanahmet area have wi-fi Internet access in thier lobby, and often in the rooms.
telephone codes
Istanbul is the only city/province in Turkey which has more than one telephone code: 212 for European side, 216 for Asian side and Princes’ Islands. When calling from one continent to the other, the usual dialing format used for intercity calls should be used, as if it’s an intercity call: 0+area code 212 or 216+7-digit telephone number. It may appear as an intercity call, but it will be treated as a local call in respect to payment. When making an intercontinental call, if you forget to dial the code, your call will not be automatically routed to the other continent number, it is likely that you will be connected to the “wrong” number which is in the same continent with you, because much of the number sets are used on both continents albeit with different codes of course. When dialing a number that is on the continent you are already standing on, only 7-digit number is enough. Don’t forget to dial the code first no matter which continent you are in if you are calling a landline number from a cell phone even if it’s a number that is in the same continent with you, though.
cope
Keep in mind that Istanbul's less-than-scrupulous hotel and restaurant owners are as market savvy as they come—they actually read the popular travel guides to Istanbul and when they get listed or favorably reviewed, they raise prices through the roof and skimp on costs. For mid-range and cheap hotels/restaurants, you may actually have a better time if you avoid places listed in your guide. Trust your nose.
stalking
Men intent on stalking foreign women may be present in tourist locations. Such men may presume that foreigners have a lot of money or liberal values and may approach foreign women in a flirtatious or forward manner looking for sex or for money either by theft or selling over-priced goods. If you are being harassed, use common sense and go to where other people are; often this is the nearest store. Creating a public scene will deter many stalkers, and these phrases may be useful in such cases:
İmdat! - "Help me!"
Ayıp! - "Rude!"
Bırak beni! - "Leave me alone!"
Dur! - "Stop it!"
Gider misin?! - "Will you go?!"
Or to really ruin him:
Beni takip etme?! - "Can you please stop stalking me?!"
Polisi ariyorum - "I am calling the cops!"
Siktir Git - "Fuck off!"
Occasionally try not to use Turkish as the stalker will like it more, just scream and run and find a safer place with crowd and police.
race, ethnicity and religion
Some service providers hotels, shop keepers, taxis, luxury night clubs's entrances today have a negative attitude towards black people, that will be because—rather than xenophobia—they might think you do not have enough money to spend, due to the fact that most of the black people who settled in Istanbul have a poor economical background.