from: Gleick, P.H. 1993. About the Data. In: Water in Crisis: A Guide to the World's
Fresh Water Resource (Ed., P.H. Gleick), Oxford University Press, New York, pp 117-119.

“Good data are hard to come by. Data are often not collected regularly and systematically.
They may not be reported in useful or consistent forms If collected, they may never be
compiled or distributed. Standards and techniques of measurements differ from region to
region, or worse from year to year Units of measure vary around the world -different
quantitation measures may have the same name, or a single measure may be called different
things in different places. Data are collected by individuals with differing skills, goals, and
intents. Some data are collected objectively; other data are collected to support different
ideological or political biases. The more we know about a data set and how it was collected,
the better equipped we will be to evaluate it and use it.”

Problems Time-series Aggregation of Data
Errors Uneven Data Inconsistencies
Differences Precision & Accuracy International


Problems with data format

Errors in the data

Difference between “measured” data and “derived” data

Time-series data and time of estimate

Uneven regional data coverage and oneven data quality

Variability, uncertainty, and illusory precision and accuracy

Aggregation of data

Inconsistent definitions, standards, and boundaries

International politics and hydrologic data

“What is in a number? Each number has a a value, such as 2.5 rather than 6.7. Each number
has a unit that defines its character, such as a volume, a flow, or a level of contamination.
Each has a level of precision, 2.5 rather than 2.531. But each also represents more than just a
physical or scientific fact. It represents something real, something tangible about the world in
which we live, something that may be far more complicated than it appears on the surface.
For example, data on per capita water availability in a country is a measure of the what is
theoretically available, not what is actually supplied to each human living there, which is
often far less. Data on potential hydroelectric resources in a country may suggest enormous
untapped energy reserves, but tapping them may be possible only at the cost of strangling our
fisheries, or ruining our Grand Canyons into flat-water reservoirs. Data on the fraction of the
population without access to basic sanitation and clean water gives a sense of the staggering
raw numbers of people without the most basic human services. But there are other meanings
hidden in this single number as well: it means 1,300 million people carmot turn on a tap in
their household and get clean water, as the readers of this book can. It means that tens or
hundreds of millions of (primarily) women and children must spend hours each day searching
for water for their basic needs And it means that millions die every year of preventable
water-related diseases.”



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