The Water Research Council classifies water supplies based on how many grains of hardness per gallon of water (g.p.g.) Measurements by grain dates to the Bronze Age as a unit of measured mass roughly based on the mass of a single seed of wheat. The chart below lists the classifications used to determine water hardness or softness.

General patterns of hardness in the United States can be found on a map developed by the U.S. Geological Survey and a map can be found on their website.² The softest waters are found in parts of New England, the South Atlantic-Gulf States, the Pacific Northwest, and Hawaii. Moderately hard waters are common in many rivers of Alaska and Tennessee, in the Great Lakes region, and the Pacific Northwest. Hard and very hard waters were found in some streams in most of the regions throughout the country. Hardest waters (greater than 1,000 mg/L) were measured in streams in Texas, New Mexico, Kansas, Arizona, and southern California. Information on how to find out about local drinking water quality can be found on the EPA website.³

TDS (salinity) is a measurement of total dissolved solids in water including inorganic (hardness, salts) and organic substances (pesticides, herbicides, etc.). The sources of salinity in water include:

• Natural minerals in rocks found in lakes, rivers, streams and aquifers
• Water from natural salt springs that enter into rivers, lakes and streams
• Agricultural fertilizers that drain from fields into rivers, lakes, streams and aquifers
• Water treatment chemicals such as chlorine that make water safe for human consumption
• Home water treatment systems, like water softeners, that treat water for hardness
• Cleaning chemicals
• Foods

Water reuse is a water conservation practice in which reclaimed water is used for a direct beneficial purpose. As examples, Arizona researchers identified the effect of TDS on water reuse to agriculture and to buildings. TDS can affect crop salt tolerance and yields and increase the need for additional water for irrigation to flush salts from root zones. It can also increase water usage by cooling towers and cause energy loss and equipment damage due to scaling.

The National Gallery of Art in Washington, DC, is a sprawling complex of buildings, underground tunnels and landscape gardens. The West wing of the galleries was designed by John Russell Pope in 1941 and is connected by an underground tunnel to the award winning East Wing, designed by I.M. Pei in 1978. Visitors to the galleries lunch in part of the underground building in front of a large, exposed water fall little knowing that this symbolic fountain also represents a complex interaction of nature with the built environment. The buildings, adjacent ice rink and gardens are engineered to use water for many multi-layered purposes.

When the East Wing was built, the water system was re-engineered for both buildings. Bulk water from the DC water supply was piped to makeup water loss in their large chilled water system. Chilled water is used in air washers for temperature control and humidification throughout the gallery. Historically a non-chemical treatment approach was used on the bulk chilled water with concern to protect the fragile and valuable artwork in the buildings.

Twenty years later, to address maintenance concerns that included the accumulation of scale and pipe corrosion, engineers began to investigate 21st century alternatives to find the best environmental alternatives for water quality while continuing to protect their concerns for air quality. According to Keith Karl, the president of Water Resources Group, the unique challenges of this project required a multi-layered approach to the design of the water conditioning system. After analyzing the source water from the D.C. water supply and the bulk circulating chilled water, their team realized that they could not use conventional treatments for biological contaminants, corrosion and scale because of the fear of having chemical fumes in the air stream for the gallery.

After extensive research, they chose a template-assisted crystallization (TAC) water conditioning system to be installed on the incoming city water used to makeup the chilled water supply. This new product excels in the prevention and removal of scale, by incorporating a technology similar to a biomechanical process, to control scale formation, without the use of chemicals and without the waste typically needed by systems that have to regenerate. The TAC system was smaller than conventional water conditioning or softening units and requires very little maintenance. A TAC system transforms the dissolved calcium in the hard City water as it is introduced into the building, into harmless calcium carbonate particles.

As a preliminary study of the effectiveness of a TAC water conditioning system, engineers piloted a 30-day study on one of the air washers. They tested for water quality, odors and calcium carbonate scale. In this trial, all aspects of water quality improved and there was an immediate and estimated twenty percent reduction of scale. This test led to the engineering of additional systems that include the large lunchroom waterfall as well as conditioned water delivered to the ice skating rink and HVAC comfort cooling system.

All of the water for the complex is treated to reduce scale. In addition, as part of a multi-layered approach to water conditioning, microbial sand vortex filters and ultraviolet treatments condition water for additional high-use areas in the facilities to assure the removal of all biological contaminates. This sustainable approach allows for specific water treatments by use in the facility. The TAC unit requires less space and has the environmental advantages of reducing maintenance costs while increasing the longevity of the plumbing system. The TAC system has also improved energy efficiency of the mechanical equipment and lowered energy costs.