How to remove a applied jQuery Plugin from element

Hi, I am working in asp.net 4.5 and below are the controls in my page

i am using watermark based on one of the musassar's article[aspsinppets.com]. which is workingperfectly. but is it possible to remove the watermark based on some condition.

Ref : http://aspsnippets.com/Articles/Display-Watermark-Text-for-ASPNet-TextBox-Password-and-MultiLine-TextArea-using-jQuery-Plugin.aspx

 $(function () {

if (document.getElementById('<%=hdnNameval.ClientID %>').value == "") {
            $("[id*=txtName]").WaterMark();
        }
        else { // remove the watermark and it's class. nothhing should be highlighed on the textbox}

});

any suggestion please