Nanofiltration　(NF)　is　promising　for　replacing　reverse　osmosis　for　boron　removal　more　effectively　and　at　a　higher　energy　efficiency.　However,　the　interplay　of　steric　and　charge　effects　underlying　rejection　behaviors　of　solutes　smaller　than　the　membrane　pore　size　remained　incompletely　understood,　which　impedes　implementation.　This　study　investigated　the　influence　of　pH　and　NaCl　concentration　on　boric　acid/borate　rejection　by　the　Desal　5DK　NF　membrane,　with　acetic　acid/acetate　(comparable　size　and　charge　nature)　and　glucose　(larger　and　neutral)　serving　as　benchmarks.　Filtration　experiments　demonstrate　that　varying　pH　in　the　range　of　3–11　and　NaCl　concentration　up　to　100　mM　had　little　effect　on　glucose　rejection　(consistently　greater　than　95%),　but　affected　the　two　smaller　solutes　significantly.　Increasing　pH　from　7　to　11　led　to　15%　higher　rejection　of　charged　acetate　because　of　the　increased　charges　of　both　the　membrane　and　solute,　while　increasing　pH　from　3　to　7　gave　30%　higher　rejection　of　neutral　boric　acid　due　to　steric　effects　stemming　from　pore-size　reduction.　The　rejections　of　the　neutral　boric　acid　and　acetic　acid　were　negligibly　affected　by　NaCl　concentration,　but　rejection　decreased　by　15%　and　50%　for　the　charged　borate　and　acetate,　respectively,　due　to　salt-induced　pore-swelling.　©　2021　Elsevier　B.V.