From dams to pools to bathtubs, things that hold water big and small prompted questions from readers in week No. 3 of The Bees drought Q&A. Our team of drought reporters answers a question a day at www.sacbee.com/water, where you can submit your own question.
Why arent we building more dams to store more water, instead of wasting money on a bullet train? David LaChance, Oroville
First, a little history. There are thousands of dams in California, and most of the good dam sites have already been taken. There are not a lot of places left with a narrow slot canyon downstream of a large watershed. Most of the locations that remain require very large, expensive dams that would not yield a lot of water. This makes the economics iffy.
In the 1990s, the now-defunct CalFed Bay Delta Program undertook a detailed study to search for the best remaining dam sites across the state. It weighed topography, water yield, cost, environmental risks and other factors. Four emerged as the most promising, and are now in various stages of final study:
• Temperance Flat Reservoir, on the San Joaquin River east of Fresno. Water yield: 400,000 acre-feet. Cost: $1 billion to $1.4 billion.
• Raise Shasta Dam on the Sacramento River. Water yield: 265,000 to 634,000 acre-feet. Cost: $900 million to $1.2 billion.
• Raise Los Vaqueros Dam in Contra Costa County. Water yield: 115,000 acre-feet. Cost: $500 million.
Another proposal recently emerged to expand San Luis Reservoir near Los Banos. The dam needs to be strengthened to withstand earthquakes. State and federal officials are considering raising the dam 20 feet at the same time to create capacity for an additional 130,000 acre-feet of water. Cost: $360 million.
Once the studies are done, the next challenge is paying for these projects. That will require an act of Congress, a state bond measure, local tax increases or all of those things.
What about pools? I have a friend building a pool. While I dont want pool businesses to go out of business, I also dont think she should be filling a new pool with water this year. C.E., Sacramento
If properly maintained and covered, pools are not as big a drain as you may think. If the pool is replacing a lawn, it may actually save water use.
The average backyard swimming pool holds 18,000 to 20,000 gallons. After its filled, the pool needs water only to replace water lost to evaporation (or too much horseplay). Pools generally are not emptied unless repairs are needed or due to poor water quality (on average, every three years).
By comparison, a lawn that covers the same square footage as the average-sized pool (18 feet by 36 feet) uses more than 24,000 gallons a year in irrigation.
Lap pools are built shallow, usually about 39 to 42 inches deep, and hold much less water than standard pools. That can cut the water capacity down substantially. A 45-by-8-foot lap pool holds about 9,500 gallons.
Used pool water doesnt have to go down the drain; it can be dechlorinated and used to irrigate landscaping.
The major issue with pool water is evaporation. In summer, a pool can lose an inch a week if left uncovered. But pool covers can cut down on evaporation 40 percent to 90 percent, depending on the model. In addition, systems can be used to capture rainwater (when it does rain) to replace pool water lost to evaporation.
What uses more water a 10-minute shower or a full bath? Sam Vargas, Lancaster
The answer depends on the size of the tub, the depth of the water and the efficiency of the showerhead. But usually, the shower will use less.
Most people use about 30 gallons of water for a bath, according to industry estimates. When filled to capacity (just below the overflow), a standard bathtub holds 42 gallons, but some of that water will be displaced when you get into the tub. So, the tub is rarely filled to capacity before taking a bath.
A low-flow showerhead uses about two gallons a minute, or 20 gallons for a 10-minute shower. A standard showerhead uses 2.5 gallons a minute, or 25 gallons for 10 minutes. Either way, the shower saves water as long as you dont go past 10 minutes. The shorter the shower, the greater the savings.