I need the title of a book?

-I am trying to remember the title of a book I read when i was very young in the 90s. It was a about a boy who went to a family reunion one summer. One thing that was unique about the story is that they said the boy had a crush on his cousin. During the summer at the family reunion he falls into a lake/pond or some other kind of body of water that was contaminated with chemicals. He developed telepathic powers. He began to read his cousin's mind as well as his grandmother's. He brought his cousin to the lake where she also falls in and stays in the water for much longer than did. She became a much more powerful psycic than him. She happened to be a sociopath and tried to exert control over him. The chemicals are later cleaned up so any hope of returning to the pond/lake to gain more power was not an option. The grandmother without the kids knowledge also had developed telepathic powers she ends up saving the day by feeding him some of the chemicals mixed in some beer. Other random details*** the contamined water was easily washed off with babyoil. The grandmother's mind had spiders that weaved her thoughts so that others could read them if she would allow it. The main character ends up falling in love with his other cousin and they live out their relationship strictly within their minds. I know this isn't a lot to go on but I would really like to remember the name of this book. Any help would be appreciated.Others See Us by William Sleator

" a swamp full of toxic waste that can give those who fall into it, or accidentally ingest its waters, the ability to read minds. The narrator, sixteen-year-old Jared, has been looking forward to the annual summer get-together of his extended family at the beach. When he falls off his bike into the swamp, he begins to read the minds of those around him. His grandmother, who has the same mind-reading ability, has used it to steal money from people's bank accounts and to blackmail the neighbors into selling their house. She also blackmails Jared and his cousin Annelise to do her bidding"

http://www.encyclopedia.com/article-1G2-鈥?/a>Seems interesting..anything with chemical on it..idk honestly..So:((((((((((((|||Spiderman