Why do you need not to put water in terrarium?

You shouldn't put water directly in a terrarium because it can create excess humidity and lead to mold growth, which can harm the plants and disrupt the ecosystem. Terrariums are designed to be self-sustaining, relying on a closed environment where moisture cycles naturally through evaporation and condensation. Instead of adding water, it's better to mist the plants occasionally if needed, as this mimics natural conditions without over-saturating the soil.