Plants wilt when they are over-watered and they wilt when they are under-watered, so it can be hard to tell what’s wrong. Overwatering is the surest way to kill a plant, causing root rot and a nasty pong, so try to use pots with drainage holes; no one wants to lie in a cold bath for weeks and roots need time to breathe and dry off in-between waterings. Since terrariums don’t have drainage holes you will need to be very careful not to overwater them.
City water is not good for plants and can slow down growth. If you have space, install a rain barrel and use the captured rainwater to water your plants. Another option is to let tap water sit in buckets for a couple of days before watering, leaving the water purer, as the chlorine evaporates, and a better temperature. Watering at room temperature is a good rule of thumb as cold water can shock the system. If these options don’t appeal, you could consider investing in a water purification system for your home, such as a reverse osmosis water filter.
To decide whether your pot plants need a drink, touch the soil. If it feels sticky and looks dark, skip on the watering. If the soil feels dry, water plants with confidence ensuring the soil is soaked through. Use saucers under pots whenever possible and allow excess water to drain out of pots before placing them back on their saucers
On average, I water plants once a week in the summer and once a fortnight in the winter. Of course, each plant has different needs, so this is just a rough guide for plants in pots, not in terrariums (more about those later). It’s tempting to stick to a schedule, but I’d advise observing your plants and feeling the soil instead.