The truth about TDS maps – What’s in a number?

Black and yellow orb weaver spider hanging out in its web by a water spicket.

Most window cleaners that use pure water and water fed pole systems will have a general understanding of how TDS works and what is involved to make that pure water.

I personally live in an exceptionally hard water area and it cost me considerably more to make pure water as opposed to people who live in a Soft water areas. Recently, I decided to check out the TDS on properties in my street. I was shocked to see the difference in TDS that was as much as much as 100!

The reason I was shocked was because the house itself was only 500 meters from my current house. I decided to check the neighbors TDS with permission just to double-check and yes their TDS was about around 100 less than mine!

I have seen several TDS maps that have existed online, which had been created to help window cleaners and so I decided to check the TDS of my area against these maps only to find that these were around 50 to 60 out. This got me thinking to how accurate is TDS?

What factors will affect the reading? Can these TDS maps give bad advice?

So, I decided to check the TDS in the area’s where I clean windows. I have a large customer base in several towns. The highest TDS reading in one village was 487. The lowest reading was 293.

Now this will still require an RO to produce pure water. The issue is at 293 I wouldn’t use a water pre softener but at 487 I would.

With this new information it suddenly got me thinking. What about people that live in different areas i.e. soft water area. They may check their map online and see their TDS for example is 150 and then decide that they need to go the RO route. They may purchase RO equipment with the assumption that their TDS will actually be 150 and then, when they actually get round to checking the TDS from the tap, it may actually be less than a 100.

As we all know, if the TDS is less than 100 then we would be able to use double DI. So, checking your tap source is imperative in order to make sure you are not investing more than you should in wfp filters.

On speaking to a customer, who is actually a plumber, he explained to me the reason why there will be a huge gap in TDS readings in a small area. Old pipe versus new pipe. New build versus old build. Plastic pipe versus copper pipe. Leaks in the system. Pressure in the system.

TDS maps are kind of a good idea but it’s only to give you a general indication of whether you live in a soft medium or hard water area you would definitely need to investigate what your actual TDS is before you buy any equipment and do not assume the readings on TDS maps are in fact accurate.

When I first started window cleaning the TDS at my house was 425. The reading at this house is now down to 350 on a good day. On speaking to Anglian Water they have advised that due to leaks being fixed in the area and pipework being replaced this would cause a lower TDS so even unscheduled water board repairs to the infrastructure will effect your TDS.

If you do not have a visual aid like a colour change resin then you will have to test your pure water regularly to establish when it needs to be changed. I would advise checking your tap water regularly too.

By D. Thurlow for Window Cleaning Magazine.