A method for starting up a system for producing methyl tert-butyl ether (MTBE), wherein the system comprises: flow lines (5, 6) and a reactor, the flow lines (5, 6) configured for feeding methanol and a mixed C4 stream, comprising isobutylene and other olefinic and/or paraffinic C4s, and the reactor configured for reacting the isobutylene and methanol to produce a crude MTBE effluent comprising MTBE, unreacted isobutylene, unreacted methanol, and the other olefinic and/or paraffinic C4s; a catalytic distillation reactor for concurrently (i) reacting the unreacted isobutylene and methanol to form additional MTBE, and (ii) separating the crude MTBE to recover a bottoms fraction comprising the MTBE and an overheads fraction comprising methanol and the other olefinic and/or paraffinic C4s; an extraction column for extracting the unreacted methanol with water, producing a C4 raffinate fraction comprising the other olefinic and/or paraffinic C4s, and an extract fraction comprising water and methanol; a distillation column for separating the extract fraction to recover an overheads fraction comprising methanol and a bottoms fraction comprising water; the method comprising: feeding aerated water having an oxygen content of greater than 50 ppbw to the distillation column (17; 33); distilling the aerated water in the distillation column (17; 33) to produce an oxygen-containing overheads and a bottoms fraction comprising deaerated water having less than 15 ppbw oxygen; transporting the deaerated water in the bottoms fraction to the extraction column; repeating the feeding aerated water, distilling, and transporting until the extraction column and distillation column are fully fed with deaerated water; starting up the reactor and the catalytic distillation reactor; feeding the overheads fraction comprising the methanol and the other olefinic and/or paraffinic C4s to the extraction column, transitioning the extraction column to producing the C4 raffinate fraction and the extract fraction comprising water and methanol; and feeding the extract fraction to the distillation column, transitioning the distillation column to separating the methanol from the water. flow lines (5, 6) and a reactor, the flow lines (5, 6) configured for feeding methanol and a mixed C4 stream, comprising isobutylene and other olefinic and/or paraffinic C4s, and the reactor configured for reacting the isobutylene and methanol to produce a crude MTBE effluent comprising MTBE, unreacted isobutylene, unreacted methanol, and the other olefinic and/or paraffinic C4s; a catalytic distillation reactor for concurrently (i) reacting the unreacted isobutylene and methanol to form additional MTBE, and (ii) separating the crude MTBE to recover a bottoms fraction comprising the MTBE and an overheads fraction comprising methanol and the other olefinic and/or paraffinic C4s; an extraction column for extracting the unreacted methanol with water, producing a C4 raffinate fraction comprising the other olefinic and/or paraffinic C4s, and an extract fraction comprising water and methanol; a distillation column for separating the extract fraction to recover an overheads fraction comprising methanol and a bottoms fraction comprising water; feeding aerated water having an oxygen content of greater than 50 ppbw to the distillation column (17; 33); distilling the aerated water in the distillation column (17; 33) to produce an oxygen-containing overheads and a bottoms fraction comprising deaerated water having less than 15 ppbw oxygen; transporting the deaerated water in the bottoms fraction to the extraction column; repeating the feeding aerated water, distilling, and transporting until the extraction column and distillation column are fully fed with deaerated water; starting up the reactor and the catalytic distillation reactor; feeding the overheads fraction comprising the methanol and the other olefinic and/or paraffinic C4s to the extraction column, transitioning the extraction column to producing the C4 raffinate fraction and the extract fraction comprising water and methanol; and feeding the extract fraction to the distillation column, transitioning the distillation column to separating the methanol from the water.