The amount of water a plant requires depends on several variables including plant species, plant size, location and environmental conditions. Bearing in mind these variables, it is impossible to predict or produce an accurate watering regime for individual plant displays.
Watering little and often taking into account the growing environment (especially light levels) is considered best practice. The RHS recommend watering from below as the best approach, given a choice I would always use a sub-irrigation system but sometimes this is not possible - top splash watering is the only option. This is where plant care experience is invaluable, knowing how to water different types of plants in different environments is something that in my experience is learnt through trial and error.
So the question is how can I make sure I am not overwatering my plant ?
There are lots of visual clues to look for on a overwatered plant, such as brown tips, yellow leaves, wilting foliage, excessive leaf loss, young shoots appear shrivelled and blackened, leaves turn pale and new growth is weak, roots appear dark and mushy, stem base is soft and spongy, wet growing medium and a strong pungent odour. However the definitive way to check for overwatering is to examine and understand the plants soil moisture levels.
You need to check the soil moisture around the roots of the plant, the most scientific way of doing this to use a soil probe. Pushing your finger into the soil is not going to work, this may tell you that the surface soil is dry (or wet) but that’s all.
To use the soil probe simply insert it into the compost, twist and withdraw. You will see small plugs of compost taken from different depths, if the compost from the bottom of the probe is wet then you do not need to water the plant. If all the plugs are wet then the plant is waterlogged.
If the plants compost is wet, no oxygen can reach the roots, the roots rot and the plant wilts because it cannot absorb any more water. At first glance without checking the soil moisture somebody could easily water the plant thinking that the wilting was due to dryness !
I have come across waterlogged plants lots of times over the years, often in an office environment it turns out that a well meaning employee is watering the plant in between our maintenance visits, an inexperienced plant technician may miss this and water the plant as normal, before long the plant is waterlogged and will probably need to be replaced.
To sum up if you do not know how much water your plant needs, simply check the soil moisture levels of your plant regularly with a soil probe to be sure you are not overwatering your plant.