Will recycled water adversely impact existing or established landscapes?
We do not expect any adverse effects on established landscapes. To be safe, landscape managers should use good maintenance practices and periodically monitor plant and soil conditions. With good observation there are practical, effective measures that can be taken to prevent or minimize any problem.

What is salinity and how does it affect trees and shrubs?
Salinity is an indication of the concentration of dissolved salts in irrigation water. Salinity is the most important measure of water quality for trees and shrubs. When excess salts are added to the soil, they can cause a buildup of salts in and on a plants foliage. Most commonly dissolved salts in recycled water are associated with sodium and bicarbonate.

How does sodium affect plants?
Irrigating with water that is high in sodium can change soil structure, resulting in poor permeability. As sodium accumulates in the soil, it attaches to soil particles, forming a crust which impedes drainage. Poor drainage stresses plants and depletes the soil of needed oxygen for root growth.

How does bicarbonate affect plants?
Irrigating with water that has a high bicarbonate level can change soil structure. Recycled water high in bicarbonate will precipitate calcium and magnesium from soil water as the soil water or solution concentrates through evapotranspiration. This results in a higher proportion of sodium.

How does pH affect plants?
The pH of irrigation water can affect the availability of nutrient elements. Deficiencies or excesses of certain elements cause stress. For example, consistently high pH causes an iron and/or manganese deficiency in foliage, resulting in yellowing (chlorosis), which ultimately causes leaves and twigs to die.

Will the nutrients in recycled water help plant growth?
Typically, the nutrient levels in recycled water are more than adequate for trees and shrubs. This has the added benefit of potentially reducing the need for fertilization. Nitrogen, phosphorus, potassium and sulfur are the nutrient elements of greatest benefit through the use of recycled water.

Be aware of soil quality and drainage.
Soil quality and drainage can influence plant health when using recycled water. Heavy soils, poor drainage and compaction can create conditions that cause an accumulation of salts. Because of this, sandy soil with good drainage is better than clay soil with poor drainage. The best way to eliminate high salt levels is leaching, which requires adequate irrigation and good drainage or percolation rates. Aerating the soil on a regular basis is one practice that will help increase and maintain drainage in the root zone of plants.

Establish a systematic plant health-care program.
Plants that are properly planted, pruned, fertilized and managed for insect and disease control will grow better and stronger using any water supply, especially recycled. A few excellent sources of information about plant health care are: 1) Specifications Handbook of the Associated Landscape Contractors of Colorado, 2) A Guide to the Plant Health Care Management System, and 3) Plant Health Care for Woody Ornamentals. The latter two are available from the International Society of Arboriculture, Rocky Mountain Chapter, Denver. Also, there is information available from Colorado State University Cooperative Extension offices.

Be aware of soil pH.
Most native soils in the Denver area have a basic or alkaline pH, i.e., greater than 7.0. Most trees and shrubs tolerate a relatively wide range in soil pH. As the soil pH rises much above 7.0, however, some plants develop deficiencies in elements such as iron and manganese, causing foliage to turn yellow. Soil pH can be lowered by periodically applying sulfur above that provided by recycled water. Or, individual plants can be treated with iron or manganese to alleviate the problem and improve health.

Test water and soil.
Denver Water will keep you updated regarding the quality of its recycled water by posting results of periodic water quality tests on the Denver Water web site at www.denverwater.org. If you feel you are having any problems, soil testing can determine levels of soluble salts, bicarbonates, pH, and other constituents discussed above. Some landscape managers may choose to test soil on a yearly basis to form a foundation for soil quality. Soil samples can be sent to a Colorado State University Cooperative Extension office, Colorado State University directly, or can be processed through a private soil testing laboratory.

Evaluate irrigation methods.
Your irrigation methods can cause an increase in a plant's absorption of salts. Absorption of elements such as chloride and sodium through leaves can cause injury to some species of plants, especially when evapotranspiration rates are high. In some cases, a greater accumulation of chloride and sodium can occur through leaves than by absorption through roots. This can be minimized by sprinkling during the evening and night. In addition, redirecting sprinkler heads to avoid or minimize water directly spraying the plants will help. Other techniques to minimize problems with water spraying plants are to use low-volume heads, and adjust the spray angle or arc.

Select high-quality plants from the nursery or supplier.
Plants that are grown properly and are free of insects, diseases and wounds will be healthier. Healthy plants can withstand stresses including those of soil and water quality, related to planting and establish-ment, much better than unhealthy or improperly grown plants. Starting out with high-quality plants can make a big difference.

Select plants that are known to be moderately or highly tolerant of soil and water salinity.
The anticipated salinity of Denver Water's recycled water is low enough to never be a problem for trees and shrubs with moderate to high salt tolerance. See the plant list provided in this brochure for some suggested plant materials.