Water, Water, Everywhere
Choosing the right water from the right source is the single
factor when using many of the methods described here. Spring, stream, or pond
water-filtered or sterilized before use-are the best sources for culture water,
with a few exceptions.
Defined media; those which contain measured quantities of several minerals, salts or supplements; are generally made with distilled or deionized water. These are the only media for which distilled or deionized water are appropriate. Distilled and deionized water lack essential trace elements and cultures placed directly in either type of water will be subject to severe osmotic stress.
Occasionally aged tap water is called for. During the aging process-when tap water is left for several days in an open container-chemicals, such as chlorine, gas-off from the water rendering it somewhat more hospitable. Other treatment chemicals and pollutants may remain at sufficient levels to harm or even kill extremely sensitive organisms. Avoid tap water unless specifically recommended, or as a last resort.
When obtaining water from natural sources (ponds, streams etc.) take pains to find a
source as free of pollution as possible. Likely sources of pollutants are nearby
industries or areas of intensive agriculture.