The drainage material in the base of the container does not actually get rid of the water. It merely holds it beneath the soil level and can release it to the soil as it is required. So this reservoir of water must not be allowed to rise to danger levels and flood the soil itself.
Plants growing together in a bowl or plant community usually require less water individually than if they were growing alone, which means that the entire bowl will require less in quantity than the sum all the plants require.
The aim here should be to moisten thoroughly the whole of the soil around the root ball and to allow a tiny excess to drain into the layer of drainage material. This will be taken up by the soil above as it is needed in much the same manner as is adopted by some of the so-called automatic or self-watering pots.
If by some accident a plant has been given too much water, drain off any excess that may be lying free. The roots may still be waterlogged, so nothing can be done about this except to allow the plant to become almost bone dry before the next watering.
The principle is much the same for all of them, relying on a reservoir of water at the base of the plant which is taken up into the soil through the base of the pot by means of a wick of material or fiber glass, or through an intermediate layer of material between reservoir and soil. So long as these automatic watering systems are used reasonably and not allowed to take over completely, they can be of assistance.
For those plants which are growing in decorative pots or bowls without drainage holes, how do we ensure that the roots are not waterlogged and how often should we water? All plants growing in containers without drainage holes must have a layer of drainage material beneath their roots which will ensure that they are not perpetually standing in water.