If your home or farm is not connected to municipal water supplies, or you need more water than municipal services can provide economically, a new water well can be extremely useful. However, designing, drilling, and constructing a water well takes a lot of careful planning, and choosing a suitable diameter for a new well can be a challenge.

Defining Water Well Diameters

All residential water wells contain well casings, large metal cylinders which function as the walls of the finished well. These casings prevent the well from collapsing under its own weight, and also stop soil-borne contaminants from leaching into your water supply.

All well casings must be surrounded by several inches of concrete to prevent the casing itself from collapsing. Consequently, the drilled hole used to create a well is significantly wider than the well casing. When well industry professionals refer to well diameter , they are almost always referring to the diameter of the well casing, rather than the well itself. 

Excluding large, industrial water wells used to supply mines and factories, most water wells contain casings between four and eight inches in diameter. Four to six-inch casings tend to be the most popular for residential and agricultural users. While a 2-inch difference in diameter may seem trivial, those extra inches can have a dramatic influence on the finished well's overall performance.

Benefits of Choosing a Narrower Well

A water well with an eight-inch diameter will be able to provide more water in a shorter period of time (usually measured in gallons-per-minute or GPM) than a six-inch well. However, you might assume that an eight-inch well provides 25 percent more water than a six-inch well, and a 12-inch well would provide twice as much water as a six-inch well. This is a common misconception.

While a wider well can obviously accommodate more water, it also requires a more powerful pump to draw all that useful water to the surface. On average, doubling the diameter of a water well's casing increases its overall yield by just 10 percent , and has little or no effect on the well's water pressure and gallons-per-minute.

With that in mind, a narrow well is frequently the best choice for residential homeowners, small mixed-crop farms, and other users with relatively modest water needs. A well-constructed six-inch water well is capable of providing more than enough water for a family or for a few acres, and costs significantly less to run and maintain.

Since narrow wells require less raw materials and smaller pumps, they are also much cheaper to drill and construct. If you are constructing a water well to avoid crippling municipal water bills, drilling a narrow well will put less strain on your finances in both the short- and long-term. 

Benefits of Choosing a Wider Well

Drilling wider may only provide slight improvements in water yield, but wider casings can provide significantly more static head volume.

Static head volume refers to how much water the well can store at ground level, where it can be used immediately. The higher the well's static head volume, the more water it can provide before the wellhead runs dry and the pump has to draw more water from underground.

Wider wells with higher static head volumes are very useful if you want your well to provide water on an as-and-when basis. This usually isn't a priority if you intend to use well water for cleaning or small-scale irrigation since you can always wait a few minutes for more water to reach the wellhead. 

However, if you want to connect your water well directly to your home or farm buildings so that faucets and appliances can use the water, a wider well may be worth the extra investment. If you attach a narrower well to this type of system, you may suffer frequent water interruptions as the well's static head volume is quickly depleted and replenished; more head volume equals fewer interruptions and less inconvenience.

Of course, the best way to determine which well diameter is right for you is by consulting with experienced well drilling professionals. Don't hesitate to contact Brown & Cox for expert advice on well diameter and design.