However, it is important to note that for planning purposes and projecting water demand, the "dry" year use average - whenever in the last 10 years the most water was used, usually in the dryest year - is used, not whatever the latest year's average is. For example, while Houston's average gallons per capita per day in 1993 was 159, for water supply purposes, the dry year figure of 189 gallons per capita per day - which occured during 1986 - is used as a base, and then adjusted for conservation. Similarly, while Austin's average gallons per capita per day is 180, the dry year gallons per capita per day used for determining future demand is 221 (occurring in 1984).

Since 1986, the Texas Water Development Board has helped promote water conservation by requiring recipients of federal and state water and wastewater loans of more than $500,000 to implement a water conservation program. To date, 165 loan recipients, including the city of Houston, have been required to adopt water conservation programs. In addition, the Texas Natural Resource Conservation Commission has recently instituted rules that require the adoption of water conservation measures as a condition of receiving a permit to use state water.(46)

Estimating the amount of fresh water needed for in-stream habitat viability is problematic. There is considerable controversy, for example, about whether the federal government's in-stream flow methodology, which was developed using cold, mountainous Western rivers as models, can be applied to Texas' slow, meandering warm water streams.

The Texas Parks and Wildlife Department uses a modified form of this methodology to determine in-stream flows that should be maintained in different streams to protect aquatic life and habitat. Parks and Wildlife favors the federal government's methodology, known as the Instream Flow Incremental Methodology (IFIM) in part because it is designed to protect riffle areas. Riffle areas are the highest points in the riverbed, which tend to be where rivers run fastest and where the invertebrates and other species inhabiting the river reach their highest populations. These riffle areas are favored by some species for their spawning habitat. The Texas Water Development Board, however, favors another methodology - the Microhabitat Assessment Technique - which is designed to protect the deep pools of the river.(55)

Equally problematic is determining the inflow needs of bays and estuaries, since they depend upon these stream inflows. An estuary occurs where a river meets the sea and fresh and salt water mix. The estuary and its adjacent wetlands - coastal vegetative areas with inundated or saturated soils - provide important biological spawning grounds for marine life. They also furnish habitat for aquatic species and migratory fowl.

Estuaries, bays and related aquatic habitats contribute significantly to the state's economy. They aid navigation and provide a base for recreational and commercial fishing and boating. An estimated 1 million recreational fishermen and 20,000 commercial fishermen fish Texas' coastal waters each year, for an estimated economic impact of $2.9 billion.(56) In addition, preserving these wetlands and estuarine systems helps ensure water quality since they act as a natural filtering system for many pollutants.

At present, and Texas Parks and Wildlife Department - in conjunction with the Texas Water Development Board and the Texas Natural Resource Conservation Commission - has developed estimates of the quantities of fresh water needed to protect San Antonio Bay. Estimates for Galveston Bay and Sabine Bay are expected in late 1995, and Texas Parks and Wildlife officials expect to have a methodology and estimate for Corpus Christi Bay by 1997.(57)

Since 1985, all new surface water use permits and all amendments to existing use permits may contain provisions to reserve water for public purposes. Water right holders are required to limit their diversion of water from rivers and streams when stream flows are below a certain level. Before 1985, however, no such diversion was explicitly required. Thus, water rights for rivers like the Rio Grande have been fully appropriated without reserving any water for environmental and public purposes. Since 1986, the state has required new reservoirs that are within 200 miles of the coast to dedicate at least 5 per-cent of their firm yield for in-stream needs of aquatic habitat and the inflow needs of the bays and estuaries. The Texas Parks and Wildlife Department may help determine the appropriate amount. Proposals to construct reservoirs or dam rivers require both a state and federal permit, and the federal permit process also requires applicants to consider effects upon streamflow and habitat.