Page 330 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch08_265-296.qxd 8/2/10 9:53 PM Page 290

290 Chapter 8 Pumping, Storage, and Dual Water Systems
pipes. They build up to the point that, with products of corrosion and tuberculation, they
significantly reduce the hydraulic capacity of the pipes. If water consumers were able to
see the insides of most distribution systems, they would be encouraged to buy bottled
water, now a fast-growing trend.
Studies in Britain have compared conventional cement-lined pipe with stainless steel
pipes of various compositions to assess their comparative rates of growth of biofilms. All
of the stainless steel pipes were found to be far better than the cement-lined pipe in terms
of the rates of biofilm growth. The stainless steel pipes that are available in very small
sizes are provided from spools that carry long lengths of product, sufficient to serve the
outlying residential areas of larger cities without the problems that are now encountered.
Larger stainless steel pipes are available in considerable lengths that can be welded, thus
avoiding joints.

8.7.5 The Proposed System
The professionals engaged in providing drinking water to the public make great efforts to
ensure water of high quality, which requires considerable investments in treating the water.
However, in the last step, distribution of the water to the consumer, the water is permitted
to be seriously degraded.
We should be embarrassed by the tremendous efforts and funds we invest in providing
high-quality water only to allow it be subjected to the many problems enumerated above,
which result in increasing health risks to the public. In our efforts to address each of the
problems, we oblige the water utilities to undertake studies and remedies far beyond the
capacities of all but the very large utilities.
Just because we have inherited distribution systems created for fighting fires over two
centuries, a practice that is responsible for all of the problems, that is no reason for contin-
uing the practice into the future, especially when the only solution offered is frequent
flushing of all the pipelines. Flushing is costly in execution, relatively ineffective, and
wasteful of the treated drinking water.
A reasonable solution is available: distribution systems designed for drinking water
alone. This option has many advantages. The pipe diameters for most of the distribution
lengths would be much smaller than the current minimum sizes. Materials such as stainless
steel can largely eliminate the bane of our present systems: leaking joints.
One very great advantage is that the size of community water treatment works would
be a small fraction of what they now need to be, encouraging the use of membrane treat-
ment, which improves the drinking water quality beyond what is now available in most
communities. The result would be purer water at a lower cost. Figure 8.13 illustrates what
a new community might do to initiate such an approach to conserving its drinking water,
affording high-quality treatment and avoiding degradation in the distribution system.
What makes this approach reasonable today is that dual systems on a large scale began
to cover the United States some 40 years ago. Some 2,000 communities in the United
States and many abroad, both the largest and the smallest cities, are adopting dual systems.
They began in arid areas but they are present also in Oregon and Washington, the country’s
wettest states. In Florida, with about 48 in. per year (1,219 mm/yr) of rainfall, some 450
communities have dual systems. Their popularity is based largely on the drinking water
supply conservation they provide.
For new communities, a dual system with one system for drinking water only, and the
other for all nonpotable purposes, including fire protection, would address not only drink-
ing water supply problems, but water quality problems as well. In addition, such systems
would be far less costly than conventional systems. Communities would be able to afford