What percentage of moisture used in watering plants will end up in indoor air?

When watering plants indoors, a significant portion of the moisture used in the process does indeed evaporate and contribute to the humidity of the indoor air. This is because as the water is absorbed by the soil and plants, a portion is lost to the atmosphere through a process called transpiration. Additionally, some of the water that remains in the soil will evaporate directly from the soil surface.

In scenarios involving indoor gardening or houseplants, it's important to acknowledge that the contribution of this moisture to indoor air can be quite significant. In many cases, nearly all of the water used for watering can eventually appear in the air in the form of vapor, especially in environments where plants are consistently watered, and there is adequate light and warmth for their growth.

Understanding this is crucial for managing indoor air quality and humidity levels. While not every single drop might directly become vapor due to various factors like plant type, soil, and environmental conditions, the general concept reinforces that the majority of moisture used does end up in the indoor air, making the assertion that "all" of it contributes to indoor humidity reasonable in a broader contextual sense.