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White deposits coming from water sounds to me like hard water, which is due to minerals, primarily calcium in the water.  The calcium precipitates out of the water as calcium carbonate (the same mineral in chalk).  This causes the insoluble white deposits that you see.

Calcium carbonate is totally harmless in the quantities in water.  It mainly causes problems with appliances, and is particularly problematic with anything made of aluminum.  It can cause the water to slowly dissolve aluminum pans, cans.  But it's safe to drink.

There are numerous things in water that can make it unsafe to drink but they are mostly invisible.  Municipal water systems carefully check for many of the harmful things, making tap water very safe to drink (safer than most bottled water, actually).