How were these GPS points obtained?
The coordinates were found by through Google maps by searching for Bekkelaget Water AS. The daily capacity was found by converting the maximal capacity per second (3.9 m3/s) to the daily capacity. This number was found in the anual report for Bekkelaget RA issued by Oslo municipality. The capacity is given in 1000m3 or ML (megaliters). Also, the starting year is set to 2001 since the same annual report says it was run by the company BEVAS since then. However, the plant may be older than this.

Are there any known data gaps?
As noted above, the year of construction of the plant is uncertain. The website is not opening, but should be www.bvas.no. It is therefore not included in the data uploaded.