There are a few factors to consider when watering plants: the type of water, how often to water, and how much water to give.
Tap water is fine for most plants, but if you have hard water, it can build up minerals in the soil that can be harmful to plants. If your tap water is high in chlorine or other chemicals, it's best to let it sit out overnight before using it on plants. You can also use rainwater or distilled water for your plants.
How often you need to water depends on the plant, the size of the pot, the type of soil, and the weather. In general, watering once a week should be sufficient. However, during hot summer days or if the plant is in a sunny spot, you may need to water more frequently. Plants in pots will dry out faster than those in the ground since they have less space for roots to grow and access moisture.
When watering plants, make sure not to overwater them as this can lead to root rot and other problems. The best way to check if a plant needs watering is to stick your finger into the soil up to your first knuckle - if it feels dry then it's time to give them a drink!