Yes, you can put goldfish in tap water. However, you can’t just fill a tank with tap water and immediately drop your goldfish in. The tap water must be treated first before it’s suitable for goldfish.
You need to neutralize the chlorine, chloramine, and ammonia that may be present. Additionally, you should cycle the water to encourage beneficial bacteria growth.
Untreated tap water is full of chlorine and chloramine, which prevents waterborne bacteria from growing. While those ingredients make the water safe for humans to drink, they’re horrible for goldfish. Chlorine and chloramine can damage their lungs and kill them.
The damage sustained from untreated tap water is irreversible and almost instantaneous, so avoid placing your goldfish in untreated tap water.