One of the most important aspects of bonsai care is watering. No matter where you locate your bonsai, it will need regular, frequent watering for survival. The soil dries quickly because of the small pot, but over-watering can cause problems as well. Taking care of a bonsai requires commitment and balance. Indoor bonsai needs year-round care on a daily basis.
Place the palm of your hand on the soil. If it feels dry, the bonsai needs water. Testing this way works because the roots absorb moisture in equal amounts---similar to a sponge---throughout the planter.
Put the bonsai in the sink. Water the soil until the pot fills. Wait for the water to drain through the holes in the planter.
Water again to make sure the whole root ball received enough. Once the water drains, place the bonsai back in its usual location.
Mist the bonsai with a spray bottle of water on very dry days, especially in the winter months. Consider keeping it in a room with a humidifier or indoor water fountain to add humidity.