AJCs Virtual Frogroom: Articles: Using Rainwater

Using Rainwater for Frogs

The water which comes out of my tap has the following chemistry:

Dendrobatids and Mantellas originate from areas where the water is soft (and usually acid, since decaying vegetation produces organic acids and soft water has little buffering capacity). The physiology of these species has evolved to cope with these conditions. Does this mean that you MUST have soft acid water to keep them? Not necessarily - most captive-bred frogs are quite adaptable in the water chemistry they will accept, as long as extremes are avoided, e.g. from pH 6.5-8.0 and from 5-20°DH. But the worst thing about hard water are those 'orrible water spots on the glass...

In the UK, the majority of the population lives in areas with hard, alkaline (and sometimes polluted) tapwater - south of the Exe-Tees line. This is also true in many US cities (e.g. Los Angeles) or if you have well-water. If you have soft water flowing from your taps, you may not wish to read any more of this page - unless you are interested in being a more eco-friendly frogkeeper.

Why use rainwater?

  • Water world-wide is becoming an ever more valuable resource - demand outstrips supply. Do you want to see more countryside disappearing under reservoirs?
  • Water treatment and transportation introduces all kinds of chemicals into your water supply: chlorine or chloramine, fluoride, copper, alum (aluminium sulphate), etc.
  • Many water supplies are now polluted with nitrates, heavy metals, pesticides, chlorinated hydrocarbons, etc... Even if your water is not polluted now, you have no way of knowing if it will be next week, next month or next year.

So how do I get soft, clean water for my frogs?

If you don't have soft water on tap or are worried about pollution, you have several choices. I'm not suggesting that you should use any of these methods in particular - the choice is yours, but just for information, you could use:

  1. Peat filtration: softens and acidifies hard water, adds beneficial humic acids (antibacterial). Drawbacks:
  2. Reverse Osmosis (R.O.): a molecular sieve which removes molecules larger than water, including pollutants. Drawbacks:
  3. Deionization: a chemical magnet which removes charged ions, leaving soft, pure (?) water. Drawbacks:
  4. Rainwater! Here's how:

The lazy way...

  • Divert rainwater from your roof into some sort of holding vessel(s) - anything from a dustbin to a full-blown reservoir.
  • Collect rainwater continuously, including all the pollution.
  • Leave collection vessel uncovered so that the water becomes green and smelly, grows a nice crop of mosquitoes, and animals and small children fall in and drown.
  • Never clean your collecting vessel out!

coverTerrarium and Cage Construction and Care
Richard D. Bartlett, Patricia Bartlett, Fredric L. Frye

This book shows you five different styles of terrarium, including desert, woodland, and half land-half water. It also tells you everything you need to know about the kinds of animals you might want to live in it. Also it includes instructions for several other types of habitats such as greenhouses and ponds. (Amazon.co.UK)

The better way...

  • Buy or construct a suitable holding vessel. My setup (below) consist of a 320 litre purpose-built rain butt from a garden centre. This has a tight fitting, child-proof lid which keeps collected water dark and clean (no algae, smell, mosquitoes) and a tap. It's worth the initial expense and much cheaper than R.O. or deionization - no running costs!
  • Use a rainwater diverter on the downpipe from the roof. You can buy these from garden centres or by mail order from adverts in gardening magazines, or simply divert the outflow from the downpipe into your collecting vessel.
  • Only collect rainwater after it has been raining steadily for a while. This ensures that the collecting surface (roof & guttering) has been washed clean and also that atmospheric pollution has been reduced/removed by rain before you start collecting. Stop collecting as soon as the rain stops. If you use a 'switchable' type diverter, this is easy. Otherwise, simply switch the outflow from the downpipe from the drain into your collecting vessel when you wish to collect.
  • Use a strainer (nylon pantyhose is ideal) over the end of the input to keep leaves, moss, grit, etc out of the collecting vessel. Clean this after each collection.
  • Clean out the collecting vessel regularly - scrape/wipe the sides and siphon the sediment which inevitably collects on the bottom.
Rainwater diverter:
Rainwater diverter
320 litre collecting vessel:
water butt


Isn't rainwater polluted?
Not if you collect and store it carefully as I have explained above. I live in an urban, industrial area close to major roads :-( My house is roofed with concrete tiles. This is not a problem since the water is only in contact with the tiles for a brief time. I occasionally test my rainwater and it always comes out as:

If it was polluted, I would not have been able to keep the species listed on this site.

Do you run out of water in the summer?
Even in dry summers, I have never actually run out, although I have come close a few times. Obviously, continuity of supply depends on the rainfall where you live. Even if you do have dry summers, you can still use rainwater during the wetter parts of the year, and help save the planet. There's not much point being concerned about destruction of the rainforests and ruining the environment in your own heavily-populated country.


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