[en] The GS process for the production of heavy water was adopted in Canada because it had been proven in the USA and was the only process offering the dependability required. Economic considerations were more important in the Canadian plants than the American ones, so considerably larger plants were built. The difficulties involved in scaling up the process were underestimated, and much time was spent in the early 1970s overcoming the problems encountered. The development program proved successful, and by 1981 Canadian heavy water plants had a total capacity of 1800 Mg/a