This　paper　presents　the　modeling　of　tide-induced　groundwater　response　using　the　spacetime　collocation　approach　(SCA).　The　newly　developed　SCA　begins　with　the　consideration　of　Trefftz　basis　functions　which　are　general　solutions　of　the　governing　equation　deriving　from　the　separation　of　variables.　The　solution　of　the　groundwater　response　in　a　coastal　confined　aquifer　with　an　estuary　boundary　where　the　phase　and　amplitude　of　tide　can　vary　with　time　and　position　is　then　approximated　by　the　linear　combination　of　Trefftz　basis　functions　using　the　superposition　theorem.　The　SCA　is　validated　for　several　numerical　examples　with　analytical　solutions.　The　comparison　of　the　results　and　accuracy　for　the　SCA　with　the　time-marching　finite　difference　method　is　carried　out.　In　addition,　the　SCA　is　adopted　to　examine　the　tidal　and　groundwater　piezometer　data　at　the　Xing-Da　port,　Kaohsiung,　Taiwan.　The　results　demonstrate　the　SCA　may　obtain　highly　accurate　results.　Moreover,　it　shows　the　advantages　of　the　SCA　such　that　we　only　discretize　by　a　set　of　points　on　the　spacetime　boundary　without　tedious　mesh　generation　and　thus　significantly　enhance　the　applicability.　©　2020　by　the　authors.