The amount of water your tropical Hibiscus needs is dependent on how warm and dry your surroundings are and how big the pot is versus how big the plant is.  Remember that Hibiscus like having water over their roots but don't want to stay in wet soil constantly.  What that means is that you should water often so that the roots do not dry out completely but the pot and soil should allow for good drainage and that the plant is using the water you are giving it. 

On very warm days, it is best to water Hibiscus once a day.  The hotter the location and the longer the sun is on the plant, the more water it will want.  Watering is always best in the morning so the plant can be ready for the heat of the day.  Also, because these plants are tropical in nature, your Hibiscus will requires less water in the colder months than during the warmer growing seasons of Spring, Summer, and Fall.

Like most tropical plants, the key to a truly healthy Hibiscus is making sure that the growing medium is sharp and will drain fast and that the pot the plant is in has adequate drain holes.  Avoid heavy dark super soils.  They retain too much moisture.  Hibiscus love water over their roots but they do not like "wet feet", that is, they do not want to sit in wet soil for extended periods of time.  This is especially true in the winter. 

If your Hibiscus is in a pot outdoors, it is best not to have the pot sitting in a pan. Just let the water run right out the bottom.  If it is indoors, you probably have no choice but to use a pan to catch excess water.  In this case, after the plant is done draining, empty the pan of excess water to allow the plant to finish draining.

Usually, you can tell that your Hibiscus is well-watered when the water begins to pour out the bottom of the pot.  This should mean that the soil is holding all the water it can.  Right? Answer: Not always.

If the soil has had a chance to dry out completely, then like a dry sponge, it takes a great deal of water to re-hydrate the soil so it will accept water again.  The water will pour out the bottom immediately without actually soaking the roots.  It may be necessary to allow the pot to stand in water for a time so that the soil saturates itself again. You should not need to worry about rehydrating the soil as long as the plant has been well-watered regularly.  But if it has ever dried out, don't be fooled by the water running out the bottom.