Quick take
Distilled or very low-mineral water is the safest practical choice for minimizing white dust and scale. RO can be a good household substitute when buying distilled water constantly is inconvenient.
Why tap water creates white dust
Dissolved calcium, magnesium and other minerals can remain behind as water evaporates or be dispersed as fine particles by ultrasonic humidifiers.
Distilled water
Distillation removes most dissolved minerals and is the standard low-mineral option for reducing deposits and white dust.
Reverse osmosis
RO also lowers dissolved mineral content substantially and can be more economical for households already using a countertop or under-sink system.