Bettas need clean, safe water to live in. There is a myth perpetuated by irresponsible pet stores that bettas live their entire lives in squalid mud holes. In reality, bettas live in thousands of gallons of waters in the rice feilds and swampy areas of Asia. During the dry season, sometimes bettas are forced to live in small amounts of water, but that is for short periods of times. Bettas, like any fish, do well in large amounts of clean, fresh water.
Make sure that your water is free of chlorine, chloramines, and heavy metals. Sometimes well water can be used without any treatment, but most water, and all city water, needs a water conditioner to make it safe for fish. If you are unsure about if your water from the tap is safe or not, either call your city water company and ask about what chemicals are in the water, or have your water tested at your local pet store. If your water needs conditioning, there are several good products out there to use.
Novaqua and Amquel are popular, and can be found in most pet stores. Aquasafe is a cheaper conditioner, but I love it. It removes chloraine, chloramine, and heavy metals, and is cheaper than other conditioners. Depending on the toxicity (to fish!) of your water, you may need to use a more expensive conditioner. Again, consult your local pet store as to which conditioner would be best for your fish.
Water changes are very important to water quality. Your bettas water should never be anything but clear and free of debris. While your betta can live a suprisingly long time is yellow, filthy water, its cruel to force it to do so. The way to have clean, clear water for your betta is to do water changes when needed. A one gallon container needs either a 100% water change one time a week, or else 50% water changes two times a week. The larger the container, the less water changes you need. Therefore, a two gallon can have a 50% water change one time a week, and a five gallon can have a 50% water change every other week.
In five gallon tanks and up, you can have the tank cycle, which will eventually cut down on the amount of water changes you need to do. Cycling, in short, is where bacteria grows that changes toxic chemicals into less toxic chemicals, which are then sometimes used as food by live plants. These chemicals are also drawn out by at least monthly gravel vacuums and water changes. To learn more about cycling, click HERE . Eventually, a cycled 10 gallon tank will need only a monthly gravel vacuum and to have evaporated water added weekly.