It happens because of high estrogen levels. Dbol is a very estrogenic steroid.
You ALWAYS want to use an AI such as aromasin when using dbol to keep estrogen levels in the normal range. You can read up on aromasin more here -> https://www.evolutionary.org/aromasin-exemestane
Yes - pretty much. A good diet helps but dbol is what we term a 'wet' steroid (meaning most of the gain is water). That doesn't mean you'll hold water under the skin.
its all about estrogen control and even then, you will still likely have some going on but estrogen is very very easily converted with dbol and can get you like a water balloon... if you do use it, DO NOT exceed 30 mg per day and make sure you use aromasin with it... arimidex is usually not strong enough unless you are just not estrogen sensitive at all but most need aromasin instead of arimidex with it
If you ever run dbol you absolutely need an AI (aromasin preferably). This type of water retention is due to estrogen. Water retention from diet has a different root cause.