This clue was a bit different, as the word was in the title of the card, New springs to locks".
A spring is thought to be the most natural and fresh of all water, hence its usage on several brands of bottled water. This is not always the case though, for the spring may be in an area trodden by cattle, or the surrounding ground contaminated by carelessly discarded sewage which can flow underground for some way without being seen. In fact even when it goes straight into a river it often takes a passing human to notify the authorities so that the problem can be investigated. However, yes, many of the bottled waters are very careful with their source waters, and guard them not just with people but with electronic measuring and surveillance.
The set first appears in our original Wills reference book, part IV, as :
HOUSEHOLD HINTS (1927-30). "Wills`s Cigarettes" at top of back in Home issue. Fronts printed by letterpress in colour. Backs with descriptive text.
234. 59. "A Series of 50". Numbered 1-50. Issued 1927. Similar series issued by Player.
A. HOME ISSUE. Fronts with white borders. Backs with I.T.C. Clause.
NEW ZEALAND ISSUES. Fronts with gilt borders.
B. "Wills`s Cigarettes" at top back.
C. "Wills`" name at base of back only.
Our original World Tobacco Index describes them as
HOUSEHOLD HINTS. Sm. Nd.
1. "Wills` Cigarettes" at top of back. See W/234-5
(i) "A Series of 50"
(ii) "2nd Series of 50"
2. Album wording at top of back. (50) . See W/236.
A. Home issue - album clause with price "one penny each"
B. Irish Issue - album clause without price.