A deep well usually requires drilling and, if constructed properly, is usually protected from most biological hazards. Go to the topic Minimizing Contamination for construction tips.

Deep wells, however, often contain dissolved minerals that can affect water quality:

• High levels of calcium and magnesium create hard water.
• High levels of arsenic or fluoride can be harmful to health.
• High levels of iron, manganese, or sulphur can stain plumbing fixtures and laundry and affect the taste and smell of the water.
  

General Construction Tips for Wells

Surface Seals

Make sure that the area between the well casing and the ground is sealed.
To make a surface seal for a well:

1. Make well hole a third to a half metre (1–2 feet) larger than well casing.
2. Place dried clay or bentonite (a highly absorbent clay) alongside casing.

 The clay absorbs water and expands to act as a seal that prevents surface runoff and pathogens from entering through the outside of the well.

Well Seals

Well caps should have a tight-fitting seal to prevent contaminants from entering the well. Sanitary well seals are available for most sizes of drilled wells. The lid should be fitted with a rubber seal to prevent contamination by rodents, insects, or surface water.

If a vent cap is necessary, it should be fitted with a fine-mesh screen.

Pump House

An important part of construction is the well or pump house. The pump house should be vented to allow the escape of gases that may come from the well, and the vents should be screened against rodents and insects.

Pump houses with unsealed doors and windows make wonderful winter homes for rodents whose droppings can be the source of disease.

The pump or well house should not be used for storage of paint, gardening chemicals, oil or other possible pollutants. These substances can be very harmful even in small quantities if they enter your well.

Floodproofing

The well casing should extend a third to a half metre (1–2 feet) above the ground to prevent any chance of floodwater overflowing the top or running down the outside of the well.