A membrane treatment process, which falls between reverse osmosis and ultrafiltration on the filtration/separation spectrum. The nanofiltration process can pass more water at lower pressure operations than reverse osmosis, can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color bodies present in water, and can reject selected (typically polyvalent) salts. Nanofiltration may be used for selective removal of hardness ions in a process known as membrane softening.
NCAA
National Collegiate Athletic Association – The governing body for intercollegiate competition and the recording agent for college swimming records.
NEMA
National Electrical Manufacturers Association
NET POSITIVE SUCTION HEAD REQUIRED
The amount of head required by the pump to keep a fluid in a liquid state.
NEUTRALIZATION
The addition of either an acid to a base or a base to an acid to produce a more nearly neutral solution. The use of alkaline or basic materials to neutralize acidity of some water is common practice in water processing to prevent corrosion of metallic home plumbing.
NITRATE
An anion comprised of one nitrogen atom and three oxygen atoms. Nitrates are considered toxic in hemodialysis water and are also harmful to infants when consumed orally.
NOMINAL FILTER RATING
Filter rating indicating the approximate size particle, the majority of which will not pass through the filter. It is generally interpreted as meaning 85 percent of the particles of the size equal to the nominal filter rating will be retained by the filter.
NONSWIMMING AREA
Any portion of a pool, spa or hot tub where water depth, offset ledges or similar irregularities would prevent normal swimming activities.
NOZZLE
An ejector part/device that increases the velocity of the liquid flowing through it by creating a partial vacuum at it's throat. Atmospheric pressure causes the increase in velocity.
NPS DISCHARGE
Nonpoint Source pollution: nutrients,. sediments, toxic substances, and pathogens that degrade waterways. NPS occurs mainly through stormwater runoff.
NPSH
Net Positive Suction Head. There are two types of NPSH. NPSHR is the amount of head required by the pump to keep the liquid being pumped in a liquid state. The only way NPSHR can be changed is by changing the pumps' rotational speed or its impeller diameter. NPSHA is the amount of head available to the pump to overcome the NPSHR. NPSHA should be a larger number than NPSHR. NPSHA is affected by atmospheric pressure changes, altitude, pipe and fitting sizes, and elevation to the liquid being pumped.
NSF
National Science Foundation.
NTU (NEOPHELOMETRIC TURBIDITY UNIT)
An instrumental means of measuring water clarity based upon the intensity of light scattered by suspended particles.