When taking water samples it is extremely important to read instructions to make sure that you are reporting the correct reading (example: ammonia vs. ammonia-N or nitrate vs. nitrate-N). 

• Bulleted items indicate target levels for each of the measured conditions as determined by State Water Resources Control Board (SWRCB) or Regional Water Quality Control Board (RWQCB).

Ammonia
Toxicity increases with increasing pH and temperature. A pH/temperature chart in conjunction with a simple calculation is necessary to determine the toxic un-ionized ammonia. It is best to report ammonia as nitrogen because it is more comparable with other nitrogen compounds.

Ammonia (NH3) = Unionized (toxic form)

Ammonia-Nitrogen (NH4+) = Ionized ammonia (also referred to as Ammonium)

• RWQCB Basin Plan objective for un-ionized ammonia is 0.025 mg/l   
• Ammonia levels greater than ~0.1 mg/l usually indicate polluted waters
• Ammonium-Nitrogen concentrations should not exceed 0.5 mg/l

Conductivity
A measure of water’s potential to conduct an electric current.  The higher the conductivity the more dissolved minerals the water contains. Excess salts in soil and water inhibit water uptake and become toxic to that organism. Animal wastes, poor subsurface drainage and some fertilizers contain high levels of salt.  RWQCB Objective for central coast levels is undetermined.

• The recommended drinking water standard is less than 900 μmhos/cm

Agricultural Suitability for Irrigation Water

CA Dept. of Water Resources

Dissolved Oxygen
DO levels fluctuate seasonally and over a 24-hour period. It varies with water temperature and altitude. Cold water holds more oxygen than warm water and water holds less oxygen at higher altitudes.

• RWQCB objective for Dissolved Oxygen is 7.0 mg/l for cold water fishes and 5.0 mg/l for warm water species.

Nitrate (NO3-)
Nitrates stimulate the growth of aquatic plants that can lead to reduced oxygen levels. High nitrate levels occur in areas of extensive agriculture, animal feedlots and septic waste systems. Nitrate in irrigation water has much the same effect as soil-applied fertilizer nitrogen. Nitrate in water can be considered useable nitrogen, and, along with a conversion factor can be incorporated into grower's fertilizer program. 1 ppm NO3-N in water = 0.6 lbs of useable nitrogen in 1 acre-foot of applied water.

• The SWRCB Drinking Water Standard for Nitrate (as NO3-) is 45 mg/l
• The SWRCB Drinking Water Standard for Nitrate-nitrogen (NO3-N) is 10 mg/l
• A Nitrate-nitrogen reading greater than 2.25 mg/l in surface water is considered to be detrimental to the aquatic environment
• Nitrate (as NO3-) should not exceed 100 mg/l for livestock consumption

Pathogens
Disease-causing organisms can result in minor illnesses such as skin rash, eye and ear infections and upset stomachs. Coliform bacteria can be generated from livestock, domestic animals, faulty septic systems, sewer line failure, wildlife, and decaying plant material.

• Fecal Coliform = concentration based on a minimum of 5 samples for any 30-day period shall not exceed 200 Most Probable Number (MPN)/100 ml

• Total Coliform = RWQCB attention level is set at 10,000 MPN/100 ml for fresh water

pH
pH affects many chemical and biological processes in water. Low pH allows toxic elements and compounds to become mobile and available to aquatic plants and animals.

• 6.5 to 8.5 = Ideal water condition
• 5.0 to 6.5 AND 8.5 to 10.0 = Caution level
• <5.0 OR >10.0 = Danger level

Phosphate (ortho) (PO43-)
Monitoring phosphorus is challenging because it involves measuring very low concentrations down to 0.01 mg/l. Even such low concentrations can have a dramatic impact on streams. Phosphate can cause algal blooms that lead to reduced oxygen levels. Less sensitive methods should be used only to identify serious problem areas.

• RWQCB target value for Orthophosphate as P is 0.12 mg/l and 0.37 as Orthophosphate as PO4
• Natural levels of orthophosphate usually range from 0.005 to 0.05 mg/l

Temperature
The rates of biological and chemical processes depend on temperature. Temperature affects the oxygen content of water, rate of photosynthesis by aquatic plants, and metabolic rate of organisms.

• Max. weekly average temp for (juvenile) fish growth = 66° F for Rainbows & 64° F for Sockeye Salmon
• Max. weekly average temp for spawning = 48° F for Rainbows & 50° F for Sockeye Salmon
• Max temp for survival of short exposure (juveniles) = 75° F for Rainbows & 64° F for Sockeye

Total Dissolved Solids
A measure of dissolved minerals in a water sample. High levels can contribute to lower crop yields. The recommended drinking water standard is 500 mg/l. See Conductivity above.

• Total Dissolved Solids = 150 to 1400 mg/l (central coast objective depending on waterbody)

Conversion Factors

• μ = micro
• 1 μmho/cm = 1 μSiemen/cm
• 1 ppm (part per million) = 1 mg/l (milligram per liter)
• Convert Nitrate-Nitrogen (NO3-N) to Nitrate as NO3 = multiply by 4.43
• Convert Ammonia ion to Ammonia-Nitrogen = divide ion reading by 1.3
• Convert Ammonia-Nitrogen to Ammonia ion = multiply by 1.3
• Convert mg/l PO43- to mg/l P = multiply by 0.326
• Convert mg/l P to mg/l PO43- = multiply by 3.07
• Fahrenheit to Celsius = oF – 32, multiply this number by 0.557 = oC
• Celsius to Fahrenheit = oC x 1.8, add 32 to this number = oF
• Convert ppt to ppm = multiply by 1000
• Convert ppm to ppt = divide by 1000
• Convert ppb to ppm = divide by 1000 (1 ppb = .001 ppm)
• Convert ppm to ppb = multiply by 1000 (.001 ppm = 1 ppb)