Endomembrane trafficking and cargo delivery are vital for plant cell growth. Plant cell growth is reliant on expansion of the encasing cell wall. Such expansion requires delivery of both new cell wall material for growth and proteins to modify the cell wall. This is particularly important in cells such as root hairs where growth is polar and therefore cargo delivery must be directed to a specific domain. We show that the Arabidopsis cation chloride cotransporter (AtCCC1) is required for normal endomembrane trafficking and that Atccc1 mutants have reduced cell growth. AtCCC1 is an endomembrane localised protein which is expressed in almost all cells and transports Cl- with K+ or Na+. Atccc1 plants have shorter roots and shoots with a reduction in the length of root epidermal cells and root hairs. The rate of root hair elongation is almost half that of wildtype plants, as measured by taking time lapse videos of cell growth. The rate of endocytosis of the endocytic dye, FM4-64, is reduced in Atccc1. Delivery of proteins to the PM is defective with large reductions in the PM to cytoplasmic ratios of the PM proteins LTI6b-GFP and PIN1-GFP. Interestingly, root hair length and elongation rates can be rescued by growing the plants under hyperosmotic stress, applied through 150 mM mannitol. Atccc1 root epidermal cells also require a higher external osmolality to induce plasmolysis. We propose a new, modified model for ion and pH regulation in the TGN/EE, in which AtCCC1 is part of the regulating transport circuit. Regulation of the TGN/EE pH is important for endomembrane trafficking and cargo sorting. Maintaining the pH of the TGN/EE results in the influx of Cl- and K+ which we propose are effluxed from the TGN/EE by AtCCC1 to maintain optimal ionic and osmotic conditions in the TGN/EE.