dry well

• drywell

From dry +‎ well (in both open compound and solid compound form).

IPA^(key): /ˈdɹaɪˌwɛl/

dry well (plural dry wells)

1. (civil engineering, construction) An underground structure (for example, a pit filled with gravel) that disposes of unwanted water (most commonly surface runoff and stormwater and in some cases greywater) by holding it and dissipating it into the groundwater.

   Synonyms: absorbing well, drain well, negative well, dumb well, dead well, blind well

Do not confuse a dry well (/ˈdɹaɪˌwɛl/) with a dry well (/ˌdɹaɪˈwɛl/) in the merely collocational sense (a noun phrase versus the compound noun), that is, a well that has run dry (whether a water well or an oil well).

• rain garden
• sump