If leaf ends are turning brown, it doesn't have to mean underwatering. Actually it might be a sign of owerwatering too. In winter there is important to maintain comfortable conditions for the plants. Try to keep them in a warm room, don't keep any extra water in their centers and maybe help them get dry after watering with a small fan. Also don't water them as frequently as in summer. If weather is really gloomy, my plants are still perfectly green after 4-5 days without watering.