Reliability and quality of water isotope data collected with a low-budget rain collector

RATIONALE Low‐budget rain collectors for water isotope analysis, such as the 'ball‐in‐funnel type collector' (BiFC), are widely used in studies on stable water isotopes of rain. To date, however, an experimental quality assessment of such devices in relation to climatic factors does not exist. METHODS We used Cavity Ring‐Down Spectrometry (CRDS) to quantify the effects of evaporation on the δ18O values of reference water under controlled conditions as a function of the elapsed time between rainfall and collection for isotope analysis, the sample volume and the relative humidity (RH: 31% and 67%; 25°C). The climate chamber conditions were chosen to reflect the warm and dry end of field conditions that favor evaporative enrichment (EE). We also tested the performance of the BiFC in the field, and compared our δ2H/δ18O data obtained by isotope ratio mass spectrometry (IRMS) with those from the Swiss National Network for the Observation of Isotopes in the Water Cycle (ISOT). RESULTS The EE increased with time, with a 1‰ increase in the δ18O values after 10 days (RH: 25%; 25°C; 35 mL (corresponding to a 5 mm rain event); p