水之道（二）软水的优点和缺点

任何事物都有正反两⾯，软化⽔具有较强的洗涤去污能⼒，但是同样具有较强的溶解腐蚀能⼒；权衡利弊，本篇的是要认识它并且采⽤有效的⽅式使⽤它，避免对设备造成损伤。软⽔不含有任何⽯灰⽯，它呈酸性，具有强的溶解⼒，可以很快地腐蚀⾦属，特别在⽤⽔的管路系统。

Soft water does not contain any dissolved limestone. It is more acidic and aggressive as a solvent, and can soon erodemetals, in particular lead where this is used within a plumbing system.

硬⽔易在开⽔壶、⽔龙头⾥形成⽔垢，也容易在洗浴后的浴缸⾥形成糟粕。同时，硬⽔形成的⽔垢会破坏热⽔系统如管路、⽔箱、热⽔炉和器具如清洗机洗碗机，也会明显地减少效率。

Hard water causes the limescale that forms in kettles, around taps and also the scum that forms around the bath and basinafter use. Hard water also forms limescale deposits in hot water systems (pipework, tanks and boilers) and appliances(washing machines and dish washers); it can significantly reduce the efficiency in all these areas.

硬⽔软化的原理

判断⽔的硬度的最简单的技术是采⽤肥皂反应的⽅式看其状态；硬⽔⾥肥皂泡⽐软⽔⾥的肥皂泡要少，并伴有⽔⾥还有沉淀物。另外⼀种常见技术叫钙化，即通过浓度的变化。这些钙化后的沉淀通常是⽩⾊的，在游泳池⾥呈现絮状或⽜奶状。The most common technique to determine the hardness of water is by looking at suds formation with soap. There is lesslather formation when soap is used with hard water compared to soft water. Instead a white precipitate (soap scum) is

produced. Another way in which water manifests its hardness is scaling i.e. forming deposits through calcification that clogplumbing. These scales are usually white because calcium and magnesium are the most common sources of hardness inwater. In swimming pools, a cloudy or milky appearance characterizes hard water.

⽔的软化是去除硬⽔中的钙离⼦、镁离⼦、和其他的⾦属离⼦，从⽽使肥皂洗涤剂更⾼效地利⽤，并且延长管道的使⽤寿命。去除⽔的硬度的⽅式通常采⽤⽯灰软化和树脂离⼦交换技术。

Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting softwater is more compatible with soap and extends the lifetime of plumbing. Water softening is usually achieved using limesoftening or ion-exchange resins.

机械式软⽔机可以被安装在管道系统⾥即可持续地去除钙镁离⼦；软⽔机的⼯作是按离⼦交换进⾏的。在这个过程中，当⽔通过交换介质床，通常是含磺酸基的聚苯⼄烯颗粒；这些颗粒与钠离⼦结合处于超饱和状态；当硬⽔通过介质床时，钙镁离⼦就发⽣了离⼦交换，这些代表硬度的离⼦被介质床吸附，同时钠离⼦释放到⽔中，当介质床充满钙镁离⼦的时候，必须更换。Mechanical water softening units can be permanently installed into the plumbing system to continuously remove calciumand magnesium. Water softeners operate on the ion exchange process. In this process, water passes through a media bed,usually sulfonated polystyrene beads. The beads are supersaturated with sodium. The ion exchange process takes place ashard water passes through the softening material. The hardness minerals attach themselves to the resin beads while sodiumon the resin beads is released simultaneously into the water. When the resin becomes saturated with calcium andmagnesium, it must be recharged.

2Na(K)+CaSO4→Ca(K)2+NaSO4　　2H(K)+CaSO4→Ca(K)2+NaSO4　

Idealized image of water softening process involving replacement of calcium ions in water with sodium ions donated by acation-exchange resin.

Stephen Lower (July 2007). \"Hard water and water softening\". Retrieved 2007-10-08. 软⽔的特性

由于软⽔含有钠离⼦成分，保健医⽣建议不⽤软⽔设备去软化热⽔或者⽤来饮⽤和烹饪的冷⽔，通常在厨房⽔池上装⼀个独⽴的⽔龙头以把软⽔分开。同时，软⽔不适合⽤来浇灌植物、草坪、和园艺花草。

Because of the sodium content of softened water, some individuals may be advised by their physician, not to install watersofteners, to soften only hot water or to bypass the water softener with a cold water line to provide unsoftened water fordrinking and cooking; usually to a separate faucet at the kitchen sink. Softened water is not recommended for wateringplants, lawns, and gardens due to its sodium content.

从化学原理上来看，衡量⽔的硬度可以通过⽔中的氢离⼦和氢氧离⼦的数量来判断，也是就说氢离⼦的值即pH值；纯⽔的pH值是7⽽软⽔的pH值⼩于6.5,硬⽔的pH值⼤于8.5；也就是说软⽔呈软性，硬⽔呈碱性。

Chemically, the hardness of water is a measure of the number of hydrogen ions (acidic) and hydroxyl ions (alkaline) presentin the water, this is defined as the potential of hydrogen value or pH value. Pure water has a pH value of 7 (neutral) while softhas a value of less than 6.5 (acidic) and hard water a value greater than 8.5 pH (alkaline).

因此在空调地暖系统、热⽔系统设计中，不是所有的系统都要先将⽔软化。⾸先判断⽔的硬度范围，对于硬度较⼤的⽔，适当进⾏软化，保持系统中的⽔呈中性。1.热⽔系统中电⼦除垢设备的应⽤。

2.⽔质保护剂的使⽤

主要成分是EDTA（⼄⼆胺四⼄酸） 使得⾦属离⼦⼜可以在环境中流动，减少⽔垢的产⽣，保持⽔的中性。