Chlorine can be purchased in two formulations: calcium hypochlorite, which is a dry powder or tablet, and sodium hypochlorite, which is a liquid (commonly called chlorine bleach). Calcium hypochlorite dissolved in water or sodium hypochlorite are added to the water system through an injection pump. These pumps can be adjusted to add the prescribed amount of chlorine and are activated by the well pump. Other liquid chemicals (such as soda ash solutions) in addition to chlorine can be injected using the same pump.
The most commonly used chemical injection pump for individual water treatment is the positive displacement diaphragm pump. These pumps are equipped with: an electric motor, a piston, a diaphragm, a suction and injection valve, a chemical holding tank, and a foot valve. The motor first withdraws the piston to pull back the diaphragm. This creates a vacuum in the chamber that opens the suction valve, drawing in the chemical. The motor then drives the piston to push on the diaphragm. This forces the chemical out of the chamber, through the injection valve, and into the water line.
Maintenance of the injection pump is crucial to its reliable operation. The motor and piston must be lubricated. Because of the corrosive nature of the concentrated chlorine solutions, the valves wear out and have to be replaced. Chlorine storage containers must also be corrosion resistant and kept out of the light. The chemical tank also needs to be checked and kept full, and occasionally cleaned if chlorine solutions are prepared with powdered hypochlorite (sediment tends to accumulate in storage containers). Advantages of this type of injection pump are its ability to deliver chemicals over a wide range of injection rates and ease of adjustment.
Other types of chlorinators add chlorine tablets to the water supply, often at the well. They are called erosion and pellet chlorinators.
Erosion chlorinators consist of a canister to hold a supply of chlorine tablets and a chamber to allow water to flow over and dissolve the tablets. These units have the advantage of using chlorine tablets that are easy to handle and store. However, the chlorine dose they deliver tends to fluctuate greatly and is difficult to control. Tablet bridging can occur when the tablets get damp in the storage canister and stick together. Taping the storage canister occasionally can help break down the bridging that occurs.
Pellet chlorinators also stand on top of the well and drop chlorine tablets directly into the well. A preset number of tablets are dropped in response to water being pumped. The well must be clear of obstructions to ensure that the tablets do not become lodged before reaching water level.
The size of chlorination systems is unlimited. A few drops of chlorine can be added to a gallon of water in an emergency or on a camping trip. Yet millions of gallons of water are chlorinated daily at large water treatment plants.
Some water supplies (mostly ponds and streams) contain some natural organic chemicals from the breakdown of plants and leaves. These organic chemicals (called precursors) can combine with chlorine to form chemicals called THMs or trihalomethanes. Trihalomethanes are suspected cancer-causing agents. Activated carbon filters can be used to remove THMs.
As with chlorine bleach, both solid and liquid formulations of chlorine are irritating to the skin and are poisonous in their concentrated form. They must be carefully handled and stored. Chlorine tablets must be stored in a dry location and both liquids and solids should be stored in their original labeled container away from children and animals. All chlorine solutions should be stored in a dark place, because light can cause a photochemical reaction which reduces their potency.