How often do you water ivy?

First of all, the term "Ivy" is very common. You could have any one of a number of plants. There are many house plants that people simply call "Ivies". The most common one is usually Epipremnum aureum, known by the common names of Golden Pothos or Devils Ivy, among others. It is usually quite helpful to know the scientific name of the plant you've got so that you can find out exactly what that plant needs to grow well.

Golden pothos, the most common 'House Ivy' that I've encountered, has long trailing vines with heart shaped leaves that are usually variagated, mottled with white or yellow. If these plants are not getting enough light, they will lose their variagation because they are producing more chlorophyll.

If your plant is getting the proper amount of light, there could be any number of reasons why the leaves are turning light and dying. If you've had the plant for a long time, it may be 'pot bound'. This will cause the plant to lose its leaves and dye. Or the plant may just need to be pruned. They will lose their older leaves as they grow. Pruning the ends of the vines will stimulate new growth on the plant where it has lost leaves.

Or your plant may be starving. Have you fed it anything? Try some worm castings or compost. These are both high in nitrogen, which is what gives plants their green color and helps them grow new leaves.

Or your plant may be infested with some sort of pest or disease. Both of these problems are almost always a result of improper care of the plant, usually over-watering.

If it were my plant and I wanted to save it, I would repot it in fresh potting soil mixed with 50% compost. If the roots of the plant have spiraled around the border of its container, it's definitely pot bound. Just cut the roots on four sides and loosen them up. The plant will appreciate it. You can even cut some of the roots off! It won't hurt the plant. I promise! Your plant probably needs bright light. Don't put it in front of any AC vents. The cool air tends to dry it out. And mist it everyday.

And finally, DON"T overwater! The soil should only be as damp as a sponge that has had all the water squeezed out of it. If you think it is dry, put your finger into the soil to about 1". If it feels damp and cool, don't water it. If the soil is too hard to stick your finger into it, you should definitely repot.