Four: Substrate, the secret to humidity control...

Once you have chosen or built a proper enclosure, you must choose an ideal substrate. For frogs and toads one must chose a substrate that holds moisture, yet resists becoming saturated and moldy. In many cases a simple substrate of a piece of indoor/outdoor carpeting is idea, as is various soils or coconut products. Not to toot my own horn, but I have two articles available on the web that cover this in detail. While written for caudates, most of this applies to frogs and toads too. They can be found here:

http://www.caudata.org/cc/articles/substrate1.shtml

http://www.caudata.org/cc/articles/substrate2.shtml

In the case of most frogs and toads humidity can be maintained by misting and/or a water dish of some sort. the keeper MUST invest in a hygrometer (thats a humidity gauge!) to keep tabs on the enclosure humidity. Daily inspection is a requirement. By knowing what humidity your pet requires, you can look at the gauge and add or withhold water as needed. In most cases, with a properly ventilated tank, daily misting is sufficient.

Many keepers spend time and money building "pretty" enclosures. As a self proclaimed vivaria expert I endorse such endeavors completely as long as they meet all the requirements for the health and safety of the animals involved. Most often, I see a lack of research and extremely poor choices in substrate in such enclosures that result in the death of the inhabitants.

FIVE: Water Sources

As stated before, daily misting is usually the best and most economical way to maintain humidity in a properly ventilated enclosure. This is highly dependent on the climate the owner resides in. Dry climates need to mist more often than wet climates. Ambient temperature also is a big factor, the warmer it is the more you need to keep tabs on enclosure humidity.

In dry climates especially, often the addition of a water dish or wet sponge to the enclosure is a necessary addition to help maintain humidity, especially in properly ventilated enclosures. In wet climates the use of small computer type fans may be needed to keep a proper evaporation ratio.
micro-climates can vary from house to house and from room to room. I can guarantee my basement critter room has very different temperature and humidity averages than say, someone's second story apartment.
As a result of this, water sources can range from the simple Tupperware container of tap water to elaborate pump/filter/fountain systems with spray bars, ultrasonic misters, and foggers. It is the duty of the owner to research, measure and adapt to their individual needs.

Truth be told, in most cases a spray bottle and a dish are extremely adequate if proper ventilation and temperature control are provided.