Someone mentioned that water is calming. I've discovered that too: my husband, when shaving, will stand in front of the basin filled with water and just stare at it for the longest time! And this reminds me that a very wise friend, a schoolteacher, taught me MANY years ago that if you have a child throwing a tantrum, get them to go wash their hands. Go with them and help them hold their wrists under the cool water. It is very calming. I think I'll try that next time we have an episode!
Have others found that their spouses perseverate with some water-related activity? His avidity in watching it reminds me of our young cat who rushes to watch the toilet flush!
I don't know about the person with Alzheimer's Disease, but I sure do know that water has always calmed ME. I grew up in RI - the Ocean State - and nothing ever calmed and soothed me as much as watching those waves. I now live on a canal in Florida, and after a bad day, I can sit out on my patio, face the canal, and just looking at the water relieves the tension. I don't even get stressed anymore when the resident alligator comes swimming down the canal. That's probably because, so far, he has stayed in the canal. :)