Don't have a slide on my current pool but grew up with one. ours when i was a kid was in about 5 feet of water. personally i would feel more comfortable with at least 5' of water because often kids go head first. just mho.

sleshar,
Each size slide will have a different criteria for installation. You can look up the depths by going to the manufacturers website. It's usually in the installation manual. It will provide you with the size of the recommended slide envelope and depths.
Most slides need to dump into 4'6" of water and require a clear/open slide space of about 14'.
Your PB should provide you with this info.
Good luck.

Thank you for your helpful comments. We are actually building a custom slide so no installation manual to go to get the right number. We measured yesterday and it actually will be 4 ft deep where it dumps. I too would be more comfortable if it were at least 5. PB is willing to jackhammer out the shotcrete and redo the slope to get it to about 5 or 5.5 feet . . . . will be about $5K -$7K! We'll lose some of the flat area we had for pool volleyball etc. Deciding today! Thanks again!

We have an SR Smith Turbo Twister. Specs say 4-1/2' of water at the deepest. They also include a landing area where you need to keep diving boards out of the way. You might want to compare your slide dimensions to that one. Also, we have noticed that people tend to skid across the water so I would be more concerned about the wall across from the the slide output. The most dangerous part of the slide is the ladder. Kids goofing off fall and hit their head on concrete.