Chlorine has been a disinfection method used in public drinking water systems since the 1900s. The introduction of chlorine into public water systems created an unprecedented level of safety in public drinking water supplies, and it virtually eliminated dangerous outbreaks of diseases like typhoid and cholera. The use of chlorine for this type of public water disinfection has been hailed by many as THE major public health achievement of the 20th century.
Public water systems, however, have 24-hour monitoring, and they are required to test their water stringently and frequently (often 6+ times per day) to comply with federal regulations. They utilize chlorine gas and have massive contact tanks and storage facilities for treated water. It’s a bit different when you want to apply chlorination to a private water supply. When treating your own water, you are essentially on your own. So what’s involved?
Continuous chlorination systems generally include the following features:
- A chemical feed pump, injection device, or tablet chlorination feeder to introduce chlorine into the water
- A chlorine solution tank to allow the chlorine to mix the proper amount
- Shut-off valves to isolate the injector for cleaning/testing purposes
- A retention tank to allow contact time
- A multi-media filter to collect any suspended matter in the water
- An activated carbon filter to remove any residual chlorine and to improve taste and odor
Continuous chlorination systems generally have a metering device that feeds the chlorine in sufficient amounts to kill bacteria. Chlorine can also be used to oxidize iron and manganese from the water (which is then collected by a filter), and will also oxidize hydrogen sulfide to reduce nuisance odors. Chlorine MUST be in contact with the water at LEAST one full minute to kill all bacteria. Some viruses and other microbes require longer contact times. Ideally, chlorine contact time is about 20 minutes.
Chlorine will NOT remove nitrates, hardness, fluoride, or many other contaminants. The concentration of chlorine that is typically applied for “normal” disinfection purposes will not adequately remove protozoan cysts such as Giardia and Cryptosporodium.
The disinfecting effectiveness of chlorine depends on many factors, but most importantly the concentration of chlorine in the water and the amount of time it’s in contact with the water prior to use (contact time). The contact time required can be dependent on other factors in the water, such as water temperature, water pH, and the types of contaminants found in the water supply. When chlorine is added to the water, it reacts with microorganisms, some chemicals, and plant materials and compounds that can actually cause taste, odor, or color changes in the water. These components “tie up” some of the chlorine (called chlorine demand), and the chlorine that is left is free, or residual chlorine. One of the most important factors in chlorine disinfection is to understand the break point of the concentration of chlorine, to ensure that it’s not only meeting the chlorine demand, but that enough chlorine is left over to allow some residual disinfection. Frequent testing is required to ensure proper chlorine amounts are maintained. It’s best to talk to a water treatment professional to assist, or to perform, this testing and set-up of a continuous chlorine system.
Depending on the type of system, some chlorination systems are located in the house, but some actually use the well itself. Always keep in mind that with chlorine disinfection comes the possibility of creating disinfection by-products, such as THMS (trihalomethanes), which over time can cause illnesses such as cancer. The EPA mandates that all public water systems have less than 80 ppb (parts per billion) of THMS in treated water. Activated carbon filters can remove SOME of the by-products, but rigorous testing and advice from your water treatment professional is the best way to deal with these issues.
Using continuous chlorination for well water is a complex and relatively expensive water treatment method that requires continuous monitoring and knowledgeable management.