Water flux is decreasing with increasing cation-controlled interlayer space. Via water flux measurements and AIMD simulations, we show that both the water flux and cation-controlled interlayer space are directly correlated to the size of the hydration shell of the respective cation. The use of cations as controlled impurities with different water affinities allows us to manipulate the number of hydrogen bonds attracted to impurities on the wall of a graphenebased nanochannel and experimentally observe its effect on the water transport through graphene-based nanochannels. Further, we gain important insights into the water transport mechanism in graphene-based nanochannels in general and support the use of HP equation to describe the water transport in graphene-based nanochannels. For the intercalation of cations into the GOMs, two different preparation methods (membrane intercalation and solution intercalation) are common and gave promising rejection results in previous studies . To exclude the influence of the different methods, in this study, both methods are used to prepare cation intercalated GOMs. For that, cation intercalated GOMs were fabricated as follows (Figure ). In the first method (membrane intercalation ), the GOMs were prepared via vacuum filtration (Figure ) by filtering GO solution through a porous polymer substrate. Then these membranes were soaked in various salt solutions (Figure ). The membranes from this approach are labelled as X-M-GO, where X stands for the corresponding cation of the salt solution and M indicates that the membrane was intercalated by soaking the GOMs. In the second approach (solution intercalation ), the GO solution was mixed with the respective salt solution prior to fabricating the membranes (Figure ). Then the salt-GO mixture was filtered by vacuum filtration through a porous polymer membrane to obtain the membrane. The membranes prepared from this approach are labelled as X-S-GO. Here, S indicates that the intercalation of GO was initiated in the GO solution by mixing with respective cation X. According to previous studies, the mass increase of dry, cation intercalated GOMs was equal to the mass of intercalated salts . Therefore, the number of moles of cations inside the X-M-GO was calculated from the mass gain of the membranes after soaking the membranes in the respective salt solution. Table shows that the number of moles of cations inside the X-M-GO range from 2-7 µmol. The number of moles of cations in the X-S-GO was controlled to match the X-M-GO by adding same number of moles of respective cations into GO solution according to Table . In X-M-GO the concentration of intercalated cation is not precisely controllable. To exclude any influence of concentration differences on the water transport, a third group of samples was prepared.