Water Conditioners

This seems to be a topic that isn’t talked about as much as it should be – should we add water conditioners (dechlorinators) to our tortoise’s drinking and soaking water? The answer is absolutely not, but read on to learn why.

Chemical dechlorination is accomplished by sulfonation – and treated water is sometimes referred to as “sulfonated water.” Various dry chemicals, which are used for dechlorination, form sulfur dioxide in solution. These chemicals include sodium sulfite ( {Na}_{2}{SO}_{3} ), sodium metabisulfite ( {Na}_{2}{S}_{2}{O}_{5} ), sodium bisulfite ( {Na}{H}{S}{O}_{3} ), and the most commonly used chemical in aquaculture and reptile dechlorinators, sodium thiosulfate ( {Na}_{2}{S}_{2}{O}_{3} ) (Lind, 1995). When chlorine is dissolved in water, it hydrolyzes to form hypochlorous acid ( {H}{O}{Cl} ) and hypochlorite ions ( {O}{Cl} ). When the sulfite salts are dissolved in chlorinated water, the sulfite ion, reacts with both free and combined forms of chlorine (Helz and Nweke, 1995; WEF, 1996). For example, the chemical reaction for Sodium Thiosulfate is the following:

{ Na }_{ 2 }{ S }_{ 2 }{ O }_{ 3 }+{ Cl }_{ 2 }+{ H }_{ 2 }{ O }\quad =\quad { Na }_{ 2 }{ S }{ O }_{ 4 }+{ S }+{ 2HCl }

The common name for { Na }_{ 2 }{ S }{ O }_{ 4 }, one of the resulting products, is Sodium sulfate. This chemical, according to the National Institute of Health, may result in gastrointestinal irritation and diarrhea when ingested by humans. When poultry drank water containing 7500 mg/L sodium sulfate for 15 days, mortality was 33%. Also reported are outbreaks of poisoning in pigs due to overdosage. Resulting effects were characterized by twitching, tremors and convulsions. The most noticeable lesion at post mortem was widespread vacuolation and necrosis of cerebral cortex (U.S. National Library of Medicine, 2017). This product is clearly unsafe and toxic to ingest.

Although this subject seems to be heavily unstudied in reptiles, there are some studies that show sulfonated waste waters pose a hazard for some sensative aquatic species. For one study, a small but significant increase in striped bass mortality in dechlorinated water compared to untreated estuarine water was reported (Hall et al., 1981). In a more recent report, the freshwater invertebrate, Ceriodaphnia dubia, experienced less reproductive success in chlorinated/ dechlorinated effluent than in undisinfected effluent (Rein et al., 1992).

Sadly, I have heard of many tortoise keepers using dechlorinators in their tortoise’s drinking and soaking water. This may seem confusing because water conditioners are not harmful to fish, and are very necessary if using tap water for filling an aquarium housing fish. An interesting difference between turtles or tortoises and fish is that fish do not actually drink the water. Because the bodies of fish living in freshwater are more saline than the water they live in, water moves into their bodies by osmosis. The chemicals used for dechlorination are likely too large or not allowed to penetrate the membrane barrier. In addition, these animals breath through their gills, which can be burned by chlorine. Obviously, the care required for fish vs. tortoises are very different. However, the confusion in needing to treat water for tortoises likely originated for the idea that water turtles (similar to tortoises) live in an aquatic setting, and often times along-side fish. I can not speak of the most appropriate treatment for water in which fish live along-side aquatic turtles, but for certain we should not be confused by the misleading association between aquatics and necessity to treat the water. Aquatic turtles, do in fact, drink the water they live in and are subject to the same ill-effects as tortoises would if they were to drink chemically treated water. The best care for turtles and tortoises would be to use tap water directly, and to not worry about the presence of chlorine. Dechlorinators are absolutely unnecessary anyways, because chlorine will evaporate completely within 24 hours, and the majority evaporates if left to sit overnight.

Even before evaporation of chlorine, it should not be harmful if consumed or allowed to be in contact with turtles or tortoises during swimming or soaking. As discussed above, when chlorine dissolves in water, hypochlorous acid ( {H}{O}{Cl} ) is formed. When present in drinking water in the most common concentration of 0.2 -1 mg/L (White, 1978), it is harmless and only a very mild acid. This topic has been overly-studied for the safety of human drinking water. Both short-term exposure and long-term exposure studies with 200 to 275 times higher chlorine levels in drinking water for rats has proven to be harmless (Daniel, 1990; NTP, 1992). When we consider the lack of studies about the safety of chemical dechlorinators, it seems quite foolish to use these products.

Your next question surely is – if it really is harmful to our turtle or tortoise, how can they market this product specifically for reptiles? Don’t ask me. All I know is that as weak as the FDA system is for protecting people, it’s even weaker for pets. Public health agencies have little authority and few resources to ensure that products produced for pets are safe (FDA CVM, 2007). Moral of story, just because something is sold on the shelf at a pet store, don’t assume it’s safe to use. And definitely do not use dechlorinators in a tortoise’s drinking water!


Daniel FB et al. Comparative subchronic toxicity studies of three disinfectants. Journal of the American Water Works Association, 1990, 82:61-69.

Lewis, R.J. (1996) Sax’s Dangerous Properties of Industrial Materials. 9th ed. Volumes 1-3. New York, NY: Van Nostrand Reinhold, p. 3039

Lind, C. (1995) Wastewater Dechlorination Options. Public Works. 126 (September): 69-70.

Hall, L. W., Jr.; Burton, D. R.; Graves, W. C.; Margery, S. L. (1981) Environ. Sci. Technol. 15, 573-578.

Helz, G.R. and Nweke, A.C. (1995) Incompleteness of Wastewater Dechlorination. Environmental Science and Technology. 29: 1018-1022.

National Toxicology Program. Report on the toxicology and carcinogenesis studies of chlorinated and chloraminated water in F344/N rats and B6C3F1 mice (drinking water studies). Research Triangle Park, NC, US Department of Health and Human Services, 1992 (NTP TR 392).

Rein, D. A.; Jamesson, G. M.; Monteith, R. A. (1992) In Water Environment Federation 65th Annual Conferenceand Exposition; Water Environment Federation: Alexandria, VA; pp 461-471.

U.S. Department of Health and Human Servies. (2018) Household Products Database – Sodium formaldehyde bisulfite. National Institute of Health. Bethesda, MD. https://hpd.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=2189

U.S. National Library of Medicine. (2017) Sodium Sulfate – Hazardous Substances Databank Number 5042. National Institute of Health. Bethesda, MD. https://toxnet.nlm.nih.gov/cgi-bin/sis/search2/f?./temp/~XePm48:1

Water Environment Federation. (1996) Operation of Municipal Wastewater Treatment Plants, 5th edition, MOP 11. Alexandria, VA: Water Environment Federation

White GC. Current chlorination and dechlorination practices in the treatment of potable water, wastewater and cooling water. In: Jolley RL, ed. Water chlorination: environmental impact and health effects. Vol. 1. Ann Arbor, MI, Ann Arbor Science, 1978:1-18.