Unsafe and untreated tap water can have adverse health effects on your cockatiel because it contains chemicals, as well as biological contaminants.
The rule of thumb is, if tap water is not safe enough for humans to drink, it’s also not safe enough for pets to drink.
There are various ways to treat tap water and ensure it’s safe for your cockatiel to drink.
Boling is the cheapest and safest way to purify water. Bring covered clean water to a boil for about 1-3 minutes and let it cool.