The advantages of a behind-thewall system are that it's mounted flush to the pool wall, so it's unobtrusive, aesthetically. "We get a lot of calls from people who don't want anything with them in the pool or hanging over the deck or visible in any way," Davidson says.

Hanging Out
At a lower price point and lessinvolved to install are over-the-wall or wall-mounted units. These are typically self-contained units that are — as you might guess — mounted on the deck or the pool wall. Some types blow water and air with a large jet like those found in portable hot tubs. Others have a propeller and intake system. (Note: the two types provide noticeably different swimming experiences, so be sure to choose the one your client prefers.) Other differences may be found in the motors, some are electric, others are hydraulic.

Portability and appearance are other differentiators. Homeowners who have spent heavily on a beautiful pool will likely have strong opinions on how they want it to look. "The concept with the deck-mount is to retrofit and you want it to have as light an imprint as you can, but the fact of the matter is that you have a serious machine there," says Murdoch. "What we heard at the trade shows is, 'I don't want to see anything,' and I can appreciate that. But on the other side is the people who want this for its functionality. There are a lot of people who like cool gadgets, and this is a cool gadget for a swimmer."