Whether there is enough water in California to meet the needs of residents, businesses, agriculture, and the natural environment, now and in the future, is important to Californians. One of the tools used to assess water availability in California is the water budget, which quantifies how much water enters and leaves the state, and how it is used or stored each year. While this information is useful for tracking quantity, it does not provide any information regarding the quality of the water. The objective of this thesis is to determine whether a method can be established for defining the quality of the water in a water budget in California. To do so requires determining whether a method can be established for creating a scale of water quality using the applicable water quality definitions for the types of water in a water budget in California. That requires determining how water quality is defined. This thesis introduces a six-step method for creating a scale of water quality categories that includes water found in both the natural and built environments in California. The method involves: selecting a geographical context; collecting water quality data applicable to the selected location; compiling water quality parameter data; organising water quality parameters in a matrix; ordering the rows of water quality parameter data values to form categories of water quality; and documenting data sources and notes. This thesis also introduces a seven-step method for creating a water budget, in the form of a modified mass flow diagram, that depicts the quality of each quantity of water. The method involves: delineating the system boundary for the water balance: selecting the water budget time period to be used for analysis; collecting water quantity data applicable to the selected system boundary and time period; drawing a modified mass flow diagram; selecting and assigning a colour code to the selected water quality scale; applying the colour code representing water quality to the modified mass flow diagram; and ordering diagram slices by level of water quality. The findings indicate that a water budget that includes water quality allows for areas of more efficient use, alternatives to over-extraction, and opportunities for reuse to be identified. Viewing the quantities and qualities depicted together on the same graphic allows like quantities and qualities to be matched, revealing opportunities for meeting demand using different water sources. Adding water quality to water budgets may not only show areas where there is room for improvement, but also depict areas where there are resources and opportunities that might not have been visually obvious from a table of numbers.