var S2collection =  imageCollection.filterDate('2016-08-01','2019-04-10')
            .filterBounds(aoi)
            .filterMetadata('CLOUD_COVERAGE_ASSESSMENT', 'equals', 0);
                Map.addLayer(S2collection, {bands:['B4', 'B3', 'B2'], max:3000});

  // Function to calculate and add an NDVI band
  var addNDVI = function(image) {
   return image.addBands(image.normalizedDifference(['B8', 'B4']));
  };
  // Add NDVI band to image collection
  var S2 = S2collection.map(addNDVI);
  // Extract NDVI band and create NDVI median composite image
  var NDVI = S2.select(['nd']);
   var NDVImed = NDVI.median(); //I just changed the name of this variable ;)
    var ndvi_vis = ['#d73027', '#f46d43', '#fdae61', '#fee08b', '#d9ef8b',
       '#a6d96a'];
       Map.addLayer(NDVI, {min:0, max:0.7, palette: ndvi_vis},'NDVI');

  // Add NDWI band to image collection
  var addNDWI = function(image) {
    return image.addBands(image.normalizedDifference(['B3', 'B5']));
  };
  // Add NDWI band to image collection
  var S2S = S2collection.map(addNDWI);
  // Extract NDWI band and create NDWI median composite image
  var NDWI = S2S.select(['nd']);
   var NDWImed = NDVI.median();
    var NDWIViz = {min: 0, max: 0.5, palette: ['00FFFF', '0000FF']};
      Map.addLayer(NDWI, NDWIViz, 'NDWI', false);


  // Function to mask out NDVI
  var S2maskedVeg = function(image) {
   var NDVI = image.select(['NDVI']);
     return image.updateMask(NDVI.lte(0.15));
  };
  // Apply water and veg masking functions to image collection
  var S2MASKNDVI = S2collection.map(S2maskedVeg);

  // Function to mask out NDWI
  var S2maskedWater = function(image) {
   var NDWI = image.select(['NDWI']);
    return image.updateMask(NDWI.lte(0.15));
  };
  // Apply water and veg masking functions to image collection
  var S2maskedW = S2MASKNDVI.map(S2maskedWater);
    Map.addLayer(S2maskedW,{max:1},'S2 masked');

var S2collection =  imageCollection.filterDate('2016-08-01','2019-04-10')
            .filterBounds(aoi)
            .filterMetadata('CLOUD_COVERAGE_ASSESSMENT', 'equals', 0);
                Map.addLayer(S2collection, {bands:['B4', 'B3', 'B2'], max:3000});

// ####### DEFINE ALL FUNCTIONS #####
  // Function to calculate and add an NDVI band
  var addNDVI = function(image) {
   return image.addBands(image.normalizedDifference(['B8', 'B4']).rename('NDVI'));
  };
  // Add NDWI band to image collection
  var addNDWI = function(image) {
    return image.addBands(image.normalizedDifference(['B3', 'B5']).rename('NDWI'));
  };
  // Function to mask out NDVI
  var S2maskedVeg = function(image) {
   var NDVI = image.select(['NDVI']);
     return image.addBands(ee.Image(1).updateMask(NDVI.lte(0.15)).rename('NDVI_mask'));
  };
  // Function to mask out NDWI
  var S2maskedWater = function(image) {
   var NDWI = image.select(['NDWI']);
    return image.addBands(ee.Image(1).updateMask(NDWI.lte(0.15)).rename('NDWI_mask'));
  };

// ####### APPLY ALL FUNCTION TO THE IMAGE COLLECTION ####
// Apply water and veg masking functions to image collection
S2collection = S2collection.map(addNDWI).map(addNDVI).map(S2maskedVeg).map(S2maskedWater);
print(S2collection)