Most irons are well set up to use tap water, and it's not going to cause any long-term issues. There may be a little mineral build-up, but this is usually easy to clean. That being said, it's commonly said that using 50% tap water and 50% distilled water can be a better solution to have more pure water. While using distilled water is great, it's also expensive. Don't worry if you're only going to use tap water as this will be fine.