What are your temperatures like in your room? If you are giving them 2 liters of water every 2-3 days, you are defintely overwatering them, which will cause the wilting. Stick your finger down in the soil a little bit and see how it feels under the top layer of dirt. If it still feels moist, don't water. You want to wait until the dirt gets fairly dry before watering, the roots also need oxygen and it is hard for them to get it when drenched in water all the time, in which case, you you want to cut down on the amount of water per watering. If the soil is dry after 2 days after giving them 2L of water then your temperature is way too high, and the plants are transpiring all the water away, which will cause them to wilt as well. You really dont wan't your room to go over 85 degrees if you can help it.