Answer: The effect could be related to overwatering and/or to the chlorine or algicide in the water. These plants require a well drained location and will not tolerate soil that is saturated or sopping wet, so that may be the main cause of the defoliation.
In many areas, chlorinated pool water may only be discharged to sanitary sewer drains (not storm drains) due to the chlorine, copper and other content. There are however commercial dechlorinating chemicals your neighbor could use. You might contact your local authorities to see what the local restrictions are; your local county authorities and/or or Penn State cooperative extension should be able to help you find out.
You may find the following information about pool water helpful. (You may need to cut and paste the complete url into your browser to make it work correctly.)
I should also mention that in many areas it is illegal to flood a neighboring property by diverting water... Good luck with your shrubs!
Q&A Library Searching Tips