Treatment rooms are the little sisters of day spas in that they are a day spa but one without a pool. They often do not have water of any kind except the sort you can drink in the changing rooms. There may be no sauna or steam room, either, although you may find one, often an infrared sauna. The focus in treatment rooms is usually more utilitarian and time-limited, with many people booking single beauty treatments or body therapies and going in and out.
A spa has always traditionally been based around water. Some people believe that the word "spa" actually comes from the Latin, meaning "sanitas per aqua", or "health through water". (Other people think that a spa is just named after a particularly spa-ey Belgian town.)
So why do we include treatment rooms without pools in The Good Spa Guide? It's because good treatment rooms offer more of a spa experience than beauty salons do; you get to change into a fluffy towelling robe, drink some herbal tea, and sojourn in a relaxation room in bliss, as well as enjoy your treatment. Some treatment rooms offer "rituals", which means you get to spend a half or a whole day in a dedicated spa environment, often with a scented bath as part of the experience. If there is a treatment rooms local to you, great: you can chill out without the splashing about or the travelling about. You'll usually find treatment rooms in town centres or shopping centres, or even some large department stores.
To get the most out of your visit
Make sure you know what's on offer. If your definition of a spa means a swim is essential, you're not going to be happy with just a rose rub, however relaxing. If you want to look good, consider going to a day spa with a focus on beauty treatments and an on-site hair salon.
If you want to retreat and relax, look for treatment rooms that offer that little bit more. You'll still be able to get your hair and make-up done, as well as your eyebrows shaped and your feet pedicured. And switch off the outside world...
If you're going for a day or half-day, check what's included in your package and what's not; some packages include treatments, teas and lunch as well as use of the relaxation rooms, and these can add up to very good value.