10 Jan How to treat water that has cysts
Cysts, such as Cryptosporidium and Giardia, are protozoan parasites found in intestinal tracts of animals. The feces of infected animals contaminates surface waters such as lakes, streams and ponds, shallow wells and ground water under the influence of surface water (GUDI). Both Cryptosporidium and Giardia are protected by an outer shell that allows them to survive outside the host body for long periods of time and makes it resistant to chlorine disinfection. Human infection can occur either by consumption of contaminated water, person-to-person transmission or from farm livestock, contamination of recreational waters such as pools etc. Infection can lead to cryptosporidiosis and giardiasis, diarrheal diseases that can cause stomach cramps, dehydration, vomiting, fever etc. Older adults, children and people with weakened immune systems are especially vulnerable.
There are several residential water treatment devices/processes that may be used to treat drinking water containing Cryptosporidium and Giardia cysts. Some are designed to serve the whole house (Point Of Entry – POE) while others are designed to serve a single drinking outlet (Point Of Use – POU).
Ultraviolet Disinfection (Point of Entry)
Ultraviolet (UVC) radiation, between 200 and 280 nm wavelength (ideally at 254 nm) is absorbed by cysts resulting in damage to their genetic material in such a way that they can no longer reproduce. According to the US EPA Enhanced Surface Water Treatment LT II guidance manual, a UV dose of 22mJ/cm² can achieve a 4.0 log reduction of both cryptosporidium and giardia. UV units performance tested and certified under NSF/ANSI 55A will provide a reliable barrier against cysts. Alternatively, UV units that are independently tested to deliver the NSF/ANSI 55A dose of >40mJ/cm² can also be effectively used as a whole house protection against cysts.
Filtration (Point of Use)
Giardia is up to 20µ long, 5-15µ wide and 2-4µ thick while Cryptosporidium is 4-6µ in diameter. Therefore residential undersink or fridge filters that are 1µ absolute (>99.99% efficient) will also provide protection against cysts. Consumers should look for systems tested and certified to NSF/ANSI 53 specifically for cyst reduction. Examples of such systems include ceramic filters and activated carbon block filters.
Letting water boil for at least 1 minute kills cysts and makes water safe to drink.
Note : Chlorination is not very effective under residential conditions as it requires a contact time of at least 20 minutes with water before use with residual chlorine level of at least 0.5 PPM. Chlorination efficiency and performance varies with pH and the presence of other substances such as iron, manganese etc.
Proper maintenance and application of devices by the consumer is important to ensure ongoing performance and this may typically consist of:
• regular replacement of original manufacturer made UV lamps
• cleaning or regular replacement of filter cartridges or other replacement parts