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.

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