The minerals in tap water and unfiltered spring water can cause water stains to form in your bong. To prevent this, always use filtered water when you smoke. It's also a good idea to use filtered water when cleaning your bong, or at least rinse it with filtered water after cleaning. If you change out your bong water each day, your bong will stay much cleaner. When old water sits in your bong, mold can form. This is pretty gross on its own, but mold also means mold stains, which can make cleaning your bong a more extensive process. This is another way to keep mold from forming and ultimately avoid getting mold stains. Try to do at least a brief cleaning weekly to keep your bong squeaky clean. Since your bong is made of glass, it's susceptible to cracking and breaking if you aren't careful. When storing and traveling with your bong, consider keeping it in a protective bag or case to keep anything from happening to it.

TL;DR in Indonesian:
Gunakan air filtrasi pada bong. Ganti air di bong setiap hari. Bersihkan bong sekali seminggu. Simpan bong dalam kantung atau kotak penyimpan.