How to change value a field of preproces
You should preprocess the field output and add a class based on the value. Then to theme in css. It's a good idea to keep the images separate and business logic separate.

&lt;?php

/**
 * Implements template_preprocess_field().
 */
function acTheme_preprocess_field(&amp;$vars) {
  $element = &amp;$vars['element'];
  if ($element['#field_infraestructura'] == 'field_infraestructura') {
    $value = $vars['element']['#items'][0]['value'];
    $vars['classes_array'][] = 'type-' . drupal_clean_css_identifier($value);
  }
}

?&gt;


Take this qwith a grain of salt - I don't see the actual code and values in my debugger, but if you replace myfield_name with the name of the field, and mytheme with the theme name (all these machine names), then it should assign the classes based on the values. 

Sadly, there may be some need of tweaking this code if some mapping does not fit - so, I hope you know at least some PHP to do that.

The output classes should be somehting like class="type-agua", and then you can theme it. You need to know css, of course - there are samples in the comments under your question.