code: function getWaterLevel(stationId, startDate, endDate, params, callback) {
      if(!stationId) {
        callback(new Error("WaterFlow.getWaterLevel: stationId required"));
        return;
      }
      params = params || {};
      params.stationid = stationId;
      if(!startDate && !endDate) {
        startDate = new Date();
        startDate.setHours(startDate.getHours() - 4);
        startDate = formatDate(startDate);
        endDate = new Date();
        endDate = formatDate(endDate);
      }
      params.startdate = startDate;
      params.endDate = endDate;
      core.callApi('/waterflowservice/GetWaterLevel', params, callback);
    }
docs: Returns a list of water level measuring points given a sertain station and time interval.
  
  @memberof module:gbgcity/WaterFlow
  @param {String} stationId
  @param {String} [startDate]
  @param {String} [endData]
  @param {Function} callback The function to call with results, function({Error} error, {Object} results)/
  @see http://data.goteborg.se/WaterFlowService/help/operations/GetWaterLevel