Most standard homeowners policies include water damage, but you should still read through your policy carefully to make sure that water damage has not been excluded from your policy. Another factor that needs to be considered is whether the water damage is caused by flooding, which is not included in any standard policy. And if the roof is leaking because of repairs you have been meaning to make but haven't gotten around to, your insurance company may not pay, even for covered water damages.
Water damage caused by a recent storm or a leaking household appliance is usually covered. Storm damages are one of the default purposes for having homeowners insurance, and the risk of appliance failure, such as a water heater leaking, is part of the initial risk assessment of the home. One exception to this general rule would be if the leak is caused by an excluded peril, such as a hurricane or earthquake. In that situation, the insurance company may decline the claim, not because the damage itself is excluded but because the initial cause of the damage was. For example, if an earthquake caused a pipe in your attic to burst, then the damage could be excluded because you did not have earthquake insurance.
If the attic leak is caused by dead branches or leaves building up on your roof, the insurance company may claim that the leak is your own fault because you failed to perform necessary maintenance. In this situation, the company would cite policyholder negligence as the reason for the denial, because the debris built up slowly over time but was never removed.
The bottom line is that even though most policies include coverage for water damage, the cause of the leak could be a possible exclusion. Read your policy carefully to find out what your exclusions are, and pick up any additional coverage you may need to make sure that your home is fully protected against all possible calamities.