There has been a lot of discussion as to the meaning behind the trinity symbol, a.k.a. the "triquetra". Feel free to search for it on Wikipedia to read more about it. People get so worked up over...
Holy water is not a symbol of the holy trinity. The holy trinity has to do with the idea of Father, Son, and Holy Spirit. Holy water is used to show the "washing away" of sin.
The Father (God), Son (Jesus) and Holy Spirit.
The Trinity Symbol
http://christianity.about.com/od/symbolspictures/ig/Christian-Symbols-Glossary/Trinity--Triquetra-.htm