Hello Patrick, "DI water" is deionized water, i.e. water that has been deionized by a synthetic cathionic and anionic resin. In some instances it can be "better" than distilled water. Best, George Date: Tue, 19 Mar 2002 08:35:34 +0800 From: Patrick Ng <patrick_ng at tvbihk_com> Subject: Re: pH Probe Cleaning I'm trying out the PH controller as well. Can someone tell me what DI water is? Thanks. Patrick Ng