[{"creationDate":ISODate("2021-03-19T10:25:05.674Z"),"_id":"605870bffa87a605bf2a983a","avgPower":8241,"WaterConsumption":22,"avgTemperature":45,"shower":"5fb56ce7734b7e04b9c97c9b","user":ObjectId("5f6cb0496a8c5a0deaa1a746")},{"creationDate":ISODate("2021-03-19T10:25:05.674Z"),"_id":"605870d9fa87a605bf2a983b","avgPower":8241,"WaterConsumption":22,"avgTemperature":45,"shower":"5fb56ce7734b7e04b9c97c9b","user":ObjectId("5f6cb0496a8c5a0deaa1a746")},{"creationDate":ISODate("2021-03-17T10:25:05.674Z"),"_id":"605870ebfa87a605bf2a983c","avgPower":4300,"WaterConsumption":32,"avgTemperature":28,"shower":"5fb56d04734b7e04b9c97c9c","user":ObjectId("5f6cb0496a8c5a0deaa1a746"),}]

db.collection.aggregate([{$project:{user:1,creationDate:1,WaterConsumption:1}},{$match:{user:"5f6cb0496a8c5a0deaa1a746"}},{$group:{_id:{$dayOfMonth:"$creationDate"},waterConsumption:{$sum:"$WaterConsumption"}}}])