jQuery watermark plugin disappearing

I am in search for a good jQuery watermark plugin that work with ASP.NET and found here and downloaded it and included in the head portion

<script src="js/jquery.watermark.min.js" type="text/javascript"></script>

I have login and signup on same page and referencing them as:

<script type="text/javascript">

        $(function () {

            $("#<%= (Login1.FindControl("UserName")).ClientID %>").watermark("Enter your Username");

            $("#<%= (Login1.FindControl("Password")).ClientID %>").watermark("Enter your Password");

            $("#<%= (CreateUserWizard1.CreateUserStep.ContentTemplateContainer.FindControl("UserName")).ClientID %>").watermark("Enter your Username");

            $("#<%= (CreateUserWizard1.CreateUserStep.ContentTemplateContainer.FindControl("Password")).ClientID %>").watermark("Enter your Password");

            $("#<%= (CreateUserWizard1.CreateUserStep.ContentTemplateContainer.FindControl("ConfirmPassword")).ClientID %>").watermark("Enter your ConfirmPassword");

            $("#<%= (CreateUserWizard1.CreateUserStep.ContentTemplateContainer.FindControl("Email")).ClientID %>").watermark("Enter your Email");

        });

    </script>

Now the problem is the watermark is showing very well for all the textboxes.If I try to login then the page will be doing postback then all the watermark from the textboxes disappears .

So what do I need to do in order not to remove all of them even though there is a postback.