Learn what the two TDS readings mean, why the raw-water value can rise and how tank-type RO purification keeps drinking water separate.
Seeing two different TDS numbers on your water purifier can raise questions, especially when one changes during daily use. Reverse osmosis TDS readings are easier to understand once you know which tank each value represents. Here is a practical guide for busy households, young families and condo residents in Thailand.
In this article
- What do the two TDS numbers on the panel mean?
- Why does the raw-tank TDS rise?
- Does returned concentrate mean you are drinking waste water?
- When should you empty the raw tank?
- Frequently asked questions
What do the two TDS numbers on the panel mean?
TDS stands for total dissolved solids. It is a general measurement of dissolved substances in water, rather than an identification of specific substances.
On a tank-type RO purifier, one reading represents the water in the raw-water tank before purification. The other represents water held in the clean-water tank after it has passed through the filtration system.
The Electrolux 700 RO Hot&Cold water purifier counter top (EPWF2KCZOW) and the Electrolux 600 RO Hot water purifier counter top (EPWE2KOZOW) show raw-water and clean-water TDS separately on the control panel, with a colour water-quality indicator, so you can check water before and after filtration in one place without opening the tank or using a separate meter. The 700 and the 600 help you monitor both stages clearly.
Comparing these numbers helps you see the difference between incoming and purified water. However, TDS alone cannot determine whether water is safe, and it should not be used by itself to judge filter life. Follow the purifier's filter-life indicator and maintenance instructions instead.
Why does the raw-tank TDS rise?
Install-free tank-type RO purifiers commonly return concentrated water from the filtration process to the raw-water tank. Because this returned water contains more dissolved substances, its TDS reading may gradually rise as purification continues.
This is a normal feature of this type of recirculating system, not an indication that purified water has flowed back into the clean-water tank.
Clean water passes through four-stage RO filtration, a pre-filter and activated carbon, then the RO filter and a coconut-shell carbon post-filter, before calcium, magnesium, sodium and potassium ions are added back for taste. The system carries the WQA Gold Seal and has SGS test results for filtration of chlorine, lead, norovirus, bacteria, microplastics and BPA in the purified water.
Source-water conditions can also change, so the raw-water number may not remain identical every time you refill the tank. Focus on using and maintaining the appliance as instructed rather than interpreting one TDS value in isolation.
Does returned concentrate mean you are drinking waste water?
No. The concentrate returns to the raw-water tank and remains on the unfiltered side of the system. Water dispensed for drinking comes only from the separate clean-water tank after filtration.
Both models have a 1.5-litre clean-water tank; the 700 has a 5-litre raw-water tank and a separate 0.5-litre cold-water tank, while the 600 has a 4-litre raw-water tank. In testing, the 700's dual UVC reduced bacteria in the clean-water tank by 99.97% and in the cold-water tank by 99.88%, while the 600's UVC reduced bacteria in its clean-water tank by more than 99%.
This separation lets a countertop purifier operate without a permanent drain connection, which can be convenient in condos or rented homes where plumbing alterations may be impractical.
Ready to make purified water part of your daily routine? Explore Electrolux water purifiers.
When should you empty the raw tank?
When the low-water light appears, avoid simply topping up the remaining water. Empty the raw-water tank first, then refill it with fresh source water according to the appliance instructions.
This routine removes the concentrated water left in the raw-water tank before the next purification cycle. It also keeps everyday operation straightforward in Thailand's warm, humid climate, where regular appliance care is especially useful.
The panel also shows filter life and alerts you when replacement is due. The pre-filter and activated-carbon filter have six-month intervals and the RO filter a two-year interval. Follow the appliance alerts and manual rather than reading a change in TDS alone as a sign the filter is spent.
Frequently asked questions
Does low TDS mean the water is safe?
Not by itself. TDS measures the overall amount of dissolved solids but does not identify individual substances or microorganisms. Water safety depends on more than one numerical reading.
Why is the clean-water TDS not zero?
RO filtration reduces dissolved substances, while the post-filter adds calcium, magnesium, sodium and potassium ions through remineralisation to improve taste. The clean-water reading therefore does not need to be zero.
Does concentrate reach the glass?
No. Concentrate returns to the raw-water tank, while the water delivered to your glass comes from the separate clean-water tank.
What should I do when the low-water light shows?
Empty the remaining water from the raw-water tank before refilling it with fresh source water, following the appliance instructions. Do not use the TDS reading in place of the warning light or the care instructions.