Build a URL with a custom query string

gistfile1.phtml

public function testBuildURL()                                                         
{                                                                                      
    $url = "http://website.com/mypage/?utm=campaign_1&foo=bar";                        
    $wrongURL = $url . "?mykey=myvalue";                                               
                                                                                       
    $parsedURL = parse_url($url);                                                      
    // grab query string from URL                                                      
    $queryString = $parsedURL['query'];                                                
    $parsedQueryString = array();                                                      
    // parse query string into array                                                   
    parse_str($queryString, $parsedQueryString);                                       
    // add your custom query params                                                    
    $parsedQueryString['mykey'] = 'myvalue';                                           
    // build a query string out of the array                                           
    $newQuery = http_build_query($parsedQueryString);                                  
                                                                                       
    $parsedURL['query'] = $newQuery;                                                   
    // requires the PECL http extension                                                
    // $newURL = http_build_url("", $parsedURL);              
                                                                                       
    // alternative url build:                                                          
    $newURL = "http://website.com/mypage/?{$newQuery}";                                
                                                                                       
    echo $newURL;                                                                                                                                                                     
}