The productivity of nanofiltration plants can be significantly improved by installing a reduced number of membrane elements serially in pressure vessels [1]. A reduced number of elements per pressure vessel results in a reduction of the hydraulic pressure losses, but more pressure vessels (with a shorter length) have to be applied. The water supply companies Friesland (WLF), Oost-Brabant (WOB) and the consultant DHV Water have developed a new pressure vessel and interconnector for nanofiltration and ultra low pressure reverse osmosis plants. This new pressure vessel in combination with the new interconnector allows optimization of the system hydraulics, without the need for extra pressure vessels. Compared to a traditional design with 6 elements serially placed in pressure vessels, an annual cost reduction of approximately 10-15% for membranes and pressure vessels can be achieved with the new design. In ultrafiltration plants, pressure vessels contribute to approximately 4% of the total construction costs. Since pressure vessels are principally not needed for pressure hold because of the low feed pressures applied, the pressure vessels can be replaced by the new interconnectors. Approximately 2% of the total construction costs can be saved in this way. Water supply company Friesland applies the new pressure vessel in an ultra low pressure reverse osmosis plant, that is started-up this year. Water supply company Oost-Brabant is testing the new interconnector for application in ultrafiltration plants.