All about TDS and Water Quality 关于TDS检测与水质判定

August 21, 2018

 

TDS value comes to mind first when people talk about the water quality. As a portable and readily avaible testing kit, TDS meter is used by lots of people to check how pure the water is and if the water treated by a water filter can be safely used for drinking. However, few people knows what exactly the TDS mean and why the simple TDS testing is trustworthy.

当我们提及水质的时候,很多人第一想到的就是TDS值。作为一个简单、随手可得的检测工具,TDS笔经常被用来判断水质的好坏以及过滤后的水是否可以拿来直接饮用。然而,很少有人知道TDS究竟测量的是哪些污染物,为什么这种简单的检测方法是可信的。

 

What is TDS? 什么是TDS?[1] 

 

Total dissolved solids (TDS) is a measure of the combined content of all inorganic and organic substances contained in a liquid in molecular, ionized ormicro-granular (colloidal sol) suspended form. A TDS meter will measure all the charged ions (both positively and negatively) that are found present in the water. These ions include calcium, magnesium, nitrates, iron to name just a few. Other pollutants like chlorine and bacteria could not be tested out. So it's hard to conclude simply from the TDS reading that the tested water is good or bad, qualified or not qualified if the water source is unknown.

总溶解固体(缩写TDS),又称溶解性固体总量,测量单位为毫克/升(mg/L),表明每升水中溶有多少毫克溶解性固体。TDS值越高,表示水中含有的溶解物越多。 总溶解固体指水中全部溶质的总量,包括无机物和有机物两者的含量。但是,氯和细菌等其他污染物无法检测出来。因此,如果检测水源不明的话,单单根据TDS检测结果并不能判断测试的水是好是坏、合格还是不合格。

 

 

Why is TDS test helpful? 为什么TDS测试有帮助?

 

Now that TDS covers both good and bad things and something harmful could not be covered, will it be meaningless to do the test? The answer might be No. In the real practice, the water source is confirmed instead of being unknown. For tap water or bottled water, they are from either lakes or rivers on the surface of the earth. Most of the solids inside tested out won't be healthy minerals. So we could generally tell from the reading if the water is clean or not and compare the tested samples. Typically for the filtered water, we could use the TDS test to tell the differences from tap water. The bigger the difference is, the better the effectiveness might be.

既然TDS无法直接判定水质好坏,那么TDS检测是否毫无意义呢?答案是否定的。在实际操作中,水源是确定而不是未知的。自来水或非天然的桶装水来自于地球表面的湖泊或河流,其水样测试出来的大部分TDS都不可能是矿物质。因此,对比测试的水样,结果可以帮助我们分辨水是否干净以及哪一种更干净。对于过滤水来说,我们还可以使用TDS检测来观察过滤水和自来水的区别。往往差异越大,过滤效果越好。

 

(For the natural bottled water, things will be a bit different. Since they are either from mountains, springs or from underground whose sources have been fully testified with good things and protected. Thus, when doing the test, it's hard to compare this to tap water or treated bottled water.) 

(对于天然矿物质水来说,情况会有所不同,因为它们来自已经被证实含有对人体有益的矿物质的山区或者地下。因此,在进行TDS测试时,不能将其与自来水或经过处理的桶装水进行比较。)

 

 

Are there standards over TDS?  TDS值有对应的标准吗?

 

Actually no theoretically and yes practically. Many counties set a maximum TDS level allowed for the drinking water but the level varies a lot from nation to nation.There is no known minimum for drinking water. But there are maximum TDS restrictions(500 for EPA, 1000 for WHO). Generally, the higher the reading for the TDS is for the tap water, the more potentially for the water to be with problems.For these who want to to assess the water with TDS, the following could be some kind of reference.

理论上没有标准,但实际上是有的。很多国家规定了自来水的TDS最高数值,但国家和国家之间的规定差别很大。TDS是没有最低限值,但是有最大限值(美国EPA<500,世卫组织<1000)。一般来说,自来水的TDS读数越高,就越有可能出现问题。对于那些想要用TDS数值对水进行水质评估的人来说,以下内容可以作为参考。

 

TDS of Tap Water in Shanghai and Beijing 上海、北京的自来水TDS值

 

Shanghai Water TDS reading-We monitored the TDS readings for Shanghai tap water over the past few years. What we found over the tap water within the city proper in the past several years could be seen in the following chart.

The TDS reading of tap water in Shanghai dropped significantly these years with the upgrade of treatment facilities and change of water source from Huangpu river to Qingcaosha reservoir along Yangtze River. (For the decreased solids, thinking about the smelly Huangpu river before, no one will believe the decreased solids are healthy minerals.)

上海自来水TDS值变化-在过去几年中我们一直在监测上海自来水TDS的变化。自2010年以来,上海不但改善了水厂处理设施,采用了更严格的水质检测标准,还让超过70%的市区人口用上了长江水,所有这些都导致了自来水TDS值的大大降低。2010年前上海自来水的TDS最高是580,2012年是400左右,到现在已经是200以内了。(对于TDS读数的降低,想想以前发臭跟发黑的****浦江水,你还会认为这里面的TDS值的降低会是因为有益矿物质的减少导致的。)

 

 

Beijing Water TDS reading-As for Beijing, the water resources consist primarily of surface water, Yangtzeriver water(South-to-North Water Diversion Project) and underground water. Though a lot of efforts have been done by the Beijing government and many high-pollution factories have been shut down or move out of Beijing, the quality of municipal water is only improved a little which is far from our expectation.  

北京自来水TDS值变化-对北京来说,主要有三种水源,分别是水库水、地下水和南水北调的长江水。尽管过去几年,北京市政府采取了诸多措施来改善自来水的水质(包括关闭或者迁移高污染企业),然而所水质的改善并未达到人们的预期。[2]

 

 

Besides,according to the data from http://data.shui.cn/ and taking six typical districts for example, the annual TDS reading in Beijing is about 300, ranked as 26th nationally for water quality.

此外,根据http://data.shui.cn/和以6个典型地区为例的数据,北京每年的TDS读数约为300,在全国水质排名第26位。

 

 

What is TDS reading for Filtered Water? 一般过滤水的TDS值是多少?

 

It all depends on which kind of filtration is used. In the market, there are 2 kinds of filtration. One is in-depth filtration like the reverse osmosis ( distillation is another type of in-depth treatment, but it's mainly used industrially.) It removes virtually everything. For water through the RO or distillation based systems, the reading for TDS will be less than 50. Bottled water from treated tap water is just of this type. Distilled water reads zero while remineralized purified water reads about 30. However, all the other non-RO filters will not change TDS that much.

过滤水的TDS值一般视过滤技术而定。目前,市场上的净水器主要分为两种,一种是深度过滤设备,如RO机(蒸馏也是深度处理,但是一般用于工业生产)。深度过滤可以有效过滤水中几乎所有的杂质,TDS值一般会在50以下。非天然矿泉水源的桶装水TDS值也是如此。蒸馏水的TDS值为0,而一般经过反渗透处理的桶装水TDS值会在30左右。对于其它简单过滤器而言,过滤水的TDS值几乎不会有任何改变。

 

 

Why simple/basic filter is unable to reduce the TDS reading? 为什么其它简单设备无法改善TDS值?

 

Basic filters refer to almost all non-RO filters include carbon filter, KDF filter, ultra-filtration filter, etc, which are often found in whole house filtration syste, water softeners, shower filters, faucet filters and so on. The basic filtratio system mainly tareget at the big sized pollutants like rust, sands, chlorine and many other chemicals in the water, which means the smaller ones like metals and other charged particles can easily escape from the capture of the basic filters. That is to say, no matter how many stages of filters are used inside, the filtered water will be with almost no change for the reading of TDS. These basic filters can even increase the TDS reading when the surface of the filter is clogged up by excessive amount of pollutants if the filters fail to be changed in time. However, it does not necesssarily mean that these basic filters are not working if they are used for non-drinking purposes. 

简单过滤技术包括几乎所有的非RO过滤技术,包括活性炭、KDF、超滤等等,包括中央净水器、沐浴净水器、水龙头净水器等。这些简单过滤器主要是针对水中的大颗粒杂质如泥沙铁锈,以及余氯和其它化学物质,然而无法去除更小的杂质,包括带电粒子以及金属等--这些是TDS的主要构成。也就是说,无论简单过滤器有多少级过滤、用料多少,都无助于改善TDS值。甚至是在使用基本过滤之后,如果不按时更换滤芯,导致大量杂质附着在滤芯表面,TDS数值可能会比原水更高。但是,这并不意味着这些过滤设备没有效果。

 

 

TDS reading for Greenwave products Greenwave产品的TDS数值

 

Greenwave recommends in-depth filtration systems for drinking and cooking water and basic filtration systems for cleaning water, and we develops products that way. For our Alatai, Betta and Clavo reverse osmosis systems, the reading of TDS in the water is less than 50. For other filters with tourmaline whose purposes are mainly softening water and adding minerals, the TDS reading of the filtered water will be with no much differences.

Greenwave建议在厨房饮用水中使用深度过滤系统,在清洁水中使用基本过滤系统。我们就是遵循这个思路开发产品的。对于我们的Alatai,Betta和Clavo反渗透系统,TDS在水中的读数小于50。对于其他使用托玛琳来添加矿物质或者是软化水的净水器来说,过滤水的TDS读数相比自来水没有太大的差别。

 

 

Tips to do the test  TDS检测注意事项

 

◆ Temperature. Temperature will affect the testing results as it will affect the moving speed of the ions in the water. When doing a test, it's better to collect cold water or samples with same temperature.

控制水温。温度会影响测试结果,因为它会影响水中离子的移动速度。在做测试时,最好是用同样的常温温度的水样品。

 

◆ Time. Before collecting a sample, to make sure the sample is representative, it‘s better to let the tap run a while ( 30 seconds) first as the water inside the pipes could possibly collected something inside over a night or some time ahead.

控制时间。在收集样本之前,为了确保样本具有代表性,最好先让水龙头放水一段时间(30秒),因为管道内可能会在一段时间内堆积了一些影响测试的物质。

 

◆ Quantity. In terms of the quantity of water sample, 1 fourth or 2 fifth of a cup will be enough.

控制水量。就水样的容量而言,占容器的1/ 4或2/ 5就足够了。 

 

 

Extra notes  其他注意事项

 

◆ TDS test is good to help tell if the bottled water(not natural mineral ) is clean and if the reverse osmosis drinking water purifieris working properly. 

TDS测试有利于帮助判断桶装水(不是天然矿物质)是否干净和反渗透饮用水净化器是否工作正常。

 

◆If your bottled water (not natural mineral) or purified water from either your individual reverse osmosis filter or the centralized reverse osmosis system in your compound reads over 50, that will mean the water is fake, expired or polluted. You are not recommended to drink that water again.

如果你的桶装水(不是天然矿物类型)或经过反渗透膜过滤后读数超过50,则证明这些所谓的桶装水或者过滤水是“有问题”,不建议饮用。

 

◆TDS test is very basic. Lab tests will be still needed if you want to know what kinds of pollutants are inside and the content of each pollutant in the water. Companies like PureLiving and us all come help do the tests.

 TDS测试很基本。如果想知道水中具体是什么污染物以及每种污染物在水中的含量,则需要实验室测试。PureLiving和我们以及其它知名实验室都可以帮忙做这些测试。

 

 

Reference  参考资料 

[1] https://en.wikipedia.org/wiki/Total_dissolved_solids

[2] AndyPitt Water Quality Management of Beijingin China Tsinghua science and technology ISSN 1007-0214  11/17 pp298-305  volume 5, number 3, September 2000i

[3] http://data.shui.cn/water/result?province=110000&city=110100&area=110109&areakey=

 

 

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