Abstract: The invention relates to a simple, very economical apparatus for conditioning "aggressive" demineralized brackish water or sea water to remove CO.sub.2 and raise the pH to about 8. The invention is undemanding as to operator skill and attention and can be used economically with rather small quantities of water, such as a few thousand gallons a day. It requires no instruments or controls and utilizes inexpensive, generally available materials, principally limestone chips. The water is first sprayed at low pressure against a conical surface to cause it to film and release the bulk of the free CO.sub.2. The water is then fed upwardly through a bed of limestone chips with at least a two minute reaction time to convert the balance of the CO.sub.2 to calcium bicarbonate which is soluble and produces a pH of about 8.