Thank you for the feedback.
I have done some additional tests to test the effect of the Reflective shader > Reflection softness.
For completeness to allow an easy comparison between all the different renders I have reproduced the test renders from my earlier post
In this image the Water shader is producing the reflections using its default settings, AA set to 6, Detail set to 0.8.
White artefacts on the water surface.
[attachimg=1]
In this image the Water shader reflections are set to 0, Reflective shader is producing the reflections, AA set to 6, Detail set to 0.8.
Reflective Shader, 4 samples (default number of samples)
White artefacts on the water surface greatly reduced.
[attachimg=2]
In this image the Water shader reflections are set to 0, Reflective shader is producing the reflections, AA set to 6, Detail set to 0.8.
Reflective Shader, 16 samples
White artefacts on the water surface greatly reduced.
Very slight improvement over the previous image.
[attachimg=3]
In this image the Water shader reflections are set to 0, Reflective shader is producing the reflections, Reflection softness set to 0.01, 4 samples.
Render Settings: AA set to 6, Detail set to 0.8.
Reflections are much less noisy.
[attachimg=4]
In this image the Water shader reflections are set to 0, Reflective shader is producing the reflections, Reflection softness set to 0.005, 4 samples.
Render Settings: AA set to 6, Detail set to 0.8.
[attachimg=5]
In this image the Water shader reflections are set to 0, Reflective shader is producing the reflections, Reflection softness set to 0.001, 4 samples.
Render Settings: AA set to 6, Detail set to 0.8.
[attachimg=6]
I am very pleased with these results, using the Reflective shader with Reflection softness set to a value of 0.01 gives a good result. I could obviously improve the quality further by increasing the reflective shader sampling, and or the render Detail setting to 1, at the cost of a much longer render time.