a yard of pump water

"a yard of pump water" is a regional or dialect word meaning something which is very straight and very thin. It is most likely picked up from family, a particular part of the country, or a piece of regional media. There is nothing to worry about: dialect vocabulary is a sign of place and heritage, not of any risky behaviour. If anything, it is a nice opportunity to talk about where the word comes from and which side of the family or which place uses it.

"a yard of pump water" is regional / dialectal English meaning something which is very straight and very thin. It is mainly heard in British English (and Irish English). A more formal or neutral equivalent would be something like "something which is very straight and very thin" expressed in standard vocabulary. A common mistake is to use "a yard of pump water" outside its region; speakers from elsewhere may not understand it or may find it self-consciously local. If you are a B2 or C1 learner, it is useful to recognise this word when you hear or read it, but think carefully about whether the situation really calls for it before using it yourself.