Method & provenance
How we keep the record
The National Storm Overflow Hub shows each overflow's current state. It does not keep a history you can go back to. River Truth does: we record every spill event the Hub publishes, every 30 minutes, and when a record changes we keep the earlier version too.
Spill events recorded
268,152
Storm overflows covered
15,805
Recording since
6 May 2026
What we keep
- Every spill event published by the Hub for every water company in England and Wales, including Welsh Water's own feed, checked every 30 minutes. Each event is its own record.
- Every later change to an event. Records are often updated after they first appear, for example when an end time is added once a spill stops. We keep the earlier version as well as the latest. So far we have kept 92,022 earlier versions.
- The raw data exactly as received, since 20 September 2026. Each response from the Hub is stored unmodified, with a SHA-256 fingerprint and the address it came from.
- River flow, level and rainfall readings from the Environment Agency. We keep recent readings online and archive older ones rather than discarding them.
- Which version of our code processed each pull, so any figure on this site can be traced to the logic that produced it.
Latest recorded pull
- Source
- nsoh:dwr-cymru
- Finished
- 2026-11-05T18:30:22.064Z
- Pages stored
- 3
- SHA-256, page 1
- 7360086f53aec3120628f217e4a5b099bbc5671a705eeee9749d5f4cc3b19195
- Code version
- 5c16b30584c61e42259cb8aaee8b181c46cee152
Daily independent timestamps
Every night we list every file we stored the day before, with its SHA-256 fingerprint, and send the fingerprint of that list to two independent timestamping authorities (DigiCert and FreeTSA, using the RFC 3161 standard). Each signs it with the time. Once sealed, a day cannot be changed without the fingerprints no longer matching, and the proof does not depend on trusting us.
| Day (UTC) | Files | Manifest SHA-256 | Download |
|---|---|---|---|
| 2026-11-04 | 1,505 | 377ae536b1f14577a02815963e67d7db44d49a6d675bd9c1540fd0d938c496f9 | list · digicert · freetsa |
| 2026-11-03 | 1,507 | 4740232c4ec54b24d0a910bfe518aca31ee9397acc1d2672f77c74e9ddfe3ad3 | list · digicert · freetsa |
| 2026-11-02 | 1,762 | 5fccccd967632da72c23db69df9671e4f05cb587fccda1b2cffa298f3775a4cc | list · digicert · freetsa |
| 2026-11-01 | 1,541 | 09f6d5d80fdd5d8098d10ff7b28f78e44c85e13184bf5f13ac0d397ce15005fd | list · digicert · freetsa |
| 2026-10-31 | 1,495 | 83fc2648f9b934c8bc56d337f2e0406e145d12de90e55dba8f1c1bb8bcd3e7d2 | list · digicert · freetsa |
| 2026-10-30 | 1,522 | 1841a0183c123e3f0fed925704bb640d99abadfc017287f2dc878bff12d52d54 | list · digicert · freetsa |
| 2026-10-29 | 1,504 | edead966d40290a5d1500826eacf1b066bb7899ef33467970d6c3067a6df81c5 | list · digicert · freetsa |
| 2026-10-28 | 1,522 | a8260c41d5ac52c4d7d8ac8ade060a8b25f1f13151ca87bfb5d702f2ad4ea9b6 | list · digicert · freetsa |
| 2026-10-27 | 1,476 | 1499da6a5e45be52e14ca54cea6e0d95da7afd61fd362a19b46501cfa481aa00 | list · digicert · freetsa |
| 2026-10-26 | 1,643 | 32a5944f890476c76504d74b210e6f1294f01a83ec556a25a386ce6a1007820a | list · digicert · freetsa |
| 2026-10-25 | 1,467 | 016ba1e01bf90c1bf2a975997809458688b30b8e420de0cbab5d86e4a27d0ade | list · digicert · freetsa |
| 2026-10-24 | 1,451 | 244bac4cfaf4a91632aa9ff72f9fac54dc2ea3f268c813c062610557aba63072 | list · digicert · freetsa |
| 2026-10-23 | 1,488 | 35b5fc61ed46b4e9ca9b5dc6d6d34247b7ce33e8e9ebd6d333e30ba5559ce98e | list · digicert · freetsa |
| 2026-10-22 | 1,466 | 8cd014bb703ccc40487627598bc3fbe689cfa63cc5e03700c1fd98e372de09dc | list · digicert · freetsa |
To check a day yourself: download the list and a timestamp, then run openssl ts -verify -digest $(sha256sum manifest.txt | cut -c1-64) -in manifest.freetsa.tsr -CAfile cacert.pem using FreeTSA's published cacert.pem.
Limits
- Our own record starts in May 2026. Earlier years come from the water companies' annual returns, not from us.
- Raw responses have been stored since 20 September 2026. Before that we kept the processed records only.
- The Hub publishes the latest event for each overflow. If one overflow started and stopped twice between two of our 30-minute checks, the first of those could be missed.
- We reproduce official records and say how we computed from them. We do not assert what any company did.
Requests
Researchers, journalists, councils and legal teams can ask for an extract of the record for any overflow, company or period we hold, with the fingerprints needed to check it. Email [email protected]. Sources are listed on the credits page.