1. I've heard the water quality isn't drinkable. Does this apply to the water in hotels as well?
Better not take the risk . Indonesians normally drink bottled mineral water , so it is sold in many places , including street's kiosks .
2. Is there anything I should buy here in the States before coming to Indonesia?
There are not many things that you cannot buy in Indonesia . But maybe you may not find the same brand (medicines , for example) .
Indonesian shopping platforms : shopee.co.id , tokopedia.com , ...
3. What do you wish you'd known about Indonesia before you came here?
Be informed that you need to register your cellphone (or tablet/laptop with a sim card) and pay taxes for items valued more than US$500 .
And if you want to use an Indonesian phone number , you need to buy a Tourist Prepaid SIM card (or similar) , probably available at the airport or official providers' stores (Telkomsel , Indosat IM3 , XL Axiata , ..).
From
https://inet.detik.com/law-and-poli...hp-baru-ini-cara-dafar-imei-bea-cukai-bandara , Aug 2024 - free translation
[... To register your cellphone IMEI, first fill out the application form via the page
https://www.beacukai.go.id/register-imei.html or via the Mobile Customs application available on the Play Store. Passengers can also register their IMEI by declaring their devices on the Electronic Customs Declaration (E-CD) via the page
https://ecd.beacukai.go.id/. Proof of filling out the form in the form of a QR Code is then submitted to the Customs officer at the arrival terminal by showing the passport, boarding pass, invoice (if any), and other supporting identification. Furthermore, the Customs officer will check the fulfillment of the requirements and determine the amount of taxes. "Each passenger is given an exemption of USD500, and the excess will be subject to taxes consisting of 10% Import Duty, 11% VAT, and Income Tax (10% for those with Indonesian Tax Number/NPWP or 20% for those without NPWP).
Passengers who previously forgot to register their IMEI at the airport arrival terminal can still register the IMEI for their device at the nearest Customs Office no later than 60 days from the date of arrival. However, devices registered after leaving the airport or port of arrival area do not receive the US$500 Import Duty exemption...]
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https://www.expatindo.org/community...basics-for-those-who-are-new-to-indonesia.69/ (Indonesian basics)