This makes the patient less likely to fall. The major risk for fracture, especially hip fracture is falling. There is not a major improvement in bone mass with exercise when applied in elderly. Certainly exercise is important in youth and adolescence, and helps increase bone mass at that stage of life. To me, the most important aspect to those who are elderly is exercise for fall prevention.
Water aerobics is fine.
When one gets in the water there is less gravity on the body, so the force of impact is not as great. However, muscle contraction, in and by itself, will help maintain or stimulate bone formation. I find it difficult for a patient to do an exercise activity that they do not enjoy, and will not participate in as a long term endeavor. One is taking a diet high in calcium. So calcium rich foods, dairy products, certain vegetables such as broccoli, small fish are very high in calcium.