Stock tank
A stock tank is used to provide drinking water for animals such as cattle or horses. Stock tanks can range in size from 100 L to over 5500 L (30 to 1500 gallons) and typically are made of galvanized steel. These tanks are filled either by a pump, windpump, creek, spring, or even rely on runoff water from rain or melting snow.
There are thousands of water ponds in Texas rangelands that locals call a "tank". When the weather is hot some people use them for swimming.
Other uses
Another use of a metal (or plastic) stock tank is at a fair or other event where they are filled with ice to keep canned and bottled beverages, or even perishables such as watermelons cold. Tackle shops are known to store minnows for fishing in them. A cowboy church commonly uses a stock tank for water baptisms.
Metal stock tanks have also been used as a cheap alternative for a hot tub. Various heating methods are possible, including a submersible wood stove such as the one made by Snorkel Stoves. Another innovative heating solution (using a salvaged drip coffee maker) can be seen here
Aquatic pets
Stock tanks can also make perfect indoor habitats for aquatic pets, such as turtles, frogs, etc. For example, red eared sliders are a species of aquatic turtles that require at least 40 L of water per 25 mm of shell length (10 gallons per inch). Considering that these turtles can grow up to 300 millimetres (12 in) in length, stock tanks are the perfect alternative for those who might not be able to afford a 340 - 450 L (90-120 gallon) tank to house their pet(s).