This report is the fifth the a series of publications by the Texas Board of Water Engineers giving chemical analyses of the surface waters in the State of Texas. The samples for which data are given were collected between October 1, 1948 and September 30, 1949. During the water year 25 daily sampling stations were maintained by the Geological Survey. Sampled were collected less frequently during the year at many other points. Quality of water records for previous years can be found in the following reports: "Chemical Composition of Texas Surface Waters, 1938-1945," by W. W. Hastings, and J. H. Rowley; "Chemical Composition of Texas Surface Waters, 1946," by W. W. Hastings and B. Irelan; "Chemical Composition of Texas Surface Waters, 1947," by B. Irelan and J. R. Avrett; "Chemical Composition of Texas Surface Waters, 1948," by B. Irelan, D. E. Weaver, and J. R. Avrett. These reports may be obtained from the Texas Board of Water Engineers and Geological Survey at Austin, Texas.

Samples for chemical analysis were collected daily at or near points on streams where gaging stations are maintained for measurement of discharge. Most of the analyses were made of 10-day composites of daily samples collected for a year at each sampling point. Three composite samples were usually prepared each month by mixing together equal quantities of daily samples collected for the 1st to the 10th, from the 11th to the 20th, and during the remainder of the month. Monthly composites were made at a few stations where variation in daily conductance was small. For some streams that are subject to sudden large changes in chemical composition, composite samples were made for shorter periods on the basis of the concentration of dissolved solids as indicated by measurement of specific conductance of the daily samples.

The mean discharge for the composite period is reported in second-feet. Specific conductance values are expressed as "micromhos, K x 10 at 25° C." Silica, calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, and nitrate are reported in parts per million. The quantity of dissolved solids is given in tons per acre-foot, tons per day (if discharge records are available), and parts per million. The total and non-carbonate hardness are reported as parts per million calcium carbonate (CaCO₃).

For those analyses where sodium and potassium are reported separately, "recent sodium" will include the equivalent quantity of sodium only. In analyses where sodium and potassium were calculated and reported as a combined value, the "percent sodium" will include the equivalent quantity of sodium and potassium.

Weighted average analyses are given for most daily sampling stations. The weighted average analysis represent approximately the composition of water that would be found in a reservoir containing all the water passing a given station during the year after through mixing in the reservoir.

Samples were analyzed according to method regularly used by the Geological Survey. These methods are essentially the same or are modifications of methods described in recognized authoritative publications for mineral analysis of water samples.

These quality of water records have been collected as part of the cooperative investigations of the water resources of Texas conducted by the Geological Survey and the Texas Board of Water Engineers. Much of the work would have been impossible without the support of the following Federal State, and local agencies The United States Bureau of Reclamation, U. S. Corps of Engineers, Brazos River Conservation and Reclamation District, Lower Colorado River Authority, Red Bluff Water Power Control District, City of Amarillo, City of Abilene, and City of Forth Worth.

The investigations were under the firection of Burdge Irelan, District Chemist, Austin, Texas. Analyses of water samples were made by Clara J. Carter, Lee J. Freeman, Homer D. Smith, Dorothy M. Suttle, DeForrest E. Weaver, and Clarence T. Welborn. Calculations of weighted averages were made by James R. Avrett, Burdge Irelan, Dorothy M. Suttle, and DeForrest E. Weaver.