Although gerbils in the wild rarely or not drink at all, they need always a water bottle or a water bowl, so they can drink when they want. Because the teeth of a gerbil don't stop growing, they need regular branches of the willow or fruit trees to gnaw on. You can also give them a 'limestone for rodents'. This is also very good for nursing females. They can use the calcium for the milk for the young gerbils.
Mongolian gerbils have a social attitude and a lonely gerbil is very unhappy.
You'll have to take at least 2 Mongolian gerbils. Adult Mongolian gerbils that are strangers for each other will mostly without exception react aggressive to each other. To bring to for each other unknown gerbils together, there is the split-cage method . Mongolian gerbils are very curious and because of that they will be very quick tame. Unlike many other rodents they aren't just active by night, but also by day.