The Water From My RO Tastes Salty…….

When your RO starts to give you water which tastes salty, there are a couple of things which need to be looked into:

1) When was the last time the RO membrane was changed ?

Typically its recommended that the RO membrane installed be changed once every year. Of course this time period can vary depending on the TDS value of the raw water. If the TDS is low (<400), the membrane may last more than a year and in some cases when the TDS is very high (>1000) it may pack up in about 10 months. Nevertheless, the membrane is the most common reason for the water to taste salty. Get the membrane changed.

2) Post Carbon Needs To Be Changed

A post carbon module is typically added in between the pure water coming from the membrane and the tap. The post carbon element absorbs gases and organic material which otherwise changes the taste of the water. It also absorbs any trace chemicals which may have escaped trapping in the RO membrane. Sometimes when this module has not been changed for a while, the water may taste strange. If its been over a year, better change this module too, just to be safe.

3) The TDS Controller Needs To Be Toned Down

When the TDS controller is allowing excessive mixing of the water coming from the membrane and the UV tube, the water may taste strange. A quick way of coming to know if this is the cause, is to dial down the TDS controller to allow less water to flow through the UV tube. This will increase the water coming from the RO membrane and will lower the overall TDS value.

 

My RO Has Stopped Working…..

So, your RO has stopped functioning and you’re wondering whats going on ? Let me help you diagnose this issue.

The most common reason for a domestic RO to stop working is that there is no feed water available to the RO. This happens when the diverter valve has been switched off by mistake. But if there is feed water available to the RO, the following could be the reasons for failure to function:

1) The pressure pump has stopped working:

In case this is the issue, the best bet is to get the pump repaired. However, the pump is not always repairable. Sometimes, a new one may need to be installed. Either way, this may turn out to be an expensive proposition since the pump is the most expensive part of an RO system.

2) The adapter/smps has burned out:

If this is the case, the adapter/smps needs to be replaced. This operation can be performed easily in case you have experience changing wires in household electrical systems. The adapter is mainly required to get the pump to work since pumps in RO systems are DC pumps (Not AC). This is to prevent the chances of an electric shock.

3) The low-pressure switch has shorted out:

A low-pressure switch cuts off the RO machine in case the water pressure input to the RO is below a certain limit. This is to prevent the pump from running dry. The switch can be replaced quite easily of you know how to do common household repairs.

4) The Solenoid Valve has stopped working:

A solenoid valve cuts off water coming from the pump when the RO is switched off. This is to prevent the waste water to keep flowing from flowing into the membrane when the RO is non-operational. When the SV shorts out, it permanently shuts off, closing water supply to the membrane. This causes the RO to stop functioning.

5) The float valve is malfunctioning

The float valve shuts off the RO when the internal tank is full of water. This prevents over flowing. But when the float valve goes bad, it permanently shuts off the machine. This is a very common reason as to why an RO system stops working.

6) There is an air vacuum inside the RO

This usually happens in case one of the pipes is loose and the pump is sucking in air. This air gets trapped inside the RO’s piping and prevents it from functioning. Another reason for this could be that the pre-bowl filter is blocked and since it’s not letting water pass through, there is a vacuum being created. This vacuum prevents any water from entering the RO system.

The above six reasons are the main reasons why RO systems stop working. In case you have any questions, do leave them in the comments section.

 

What is a TDS controller ?

I’m pretty sure that anyone who has looked at an advertisement of an RO system has seen the words ‘TDS Controller’. I’d like to tell a little more about what this thing is and how it can help you.

A TDS controller, like the name suggests is a device which helps control the TDS level of the water coming out of the RO. The RO process reduces the hardness of the input water by approximately 90%. This means, that for an input of TDS 700, the output will be close to 70.

However, sometimes the source being used for the RO system itself has a low TDS value. Now water having a low TDS value, does not indicate that its pure. Also, the RO system does not just reduce the TDS, it also filters away, microbes and other contaminants from the water. Thus, the water coming from such a setup, with a low input TDS, with have a bitter taste. To prevent this, a TDS controller is installed which allows us to raise the TDS value of the output water.

Now comes the question, how does this work ?

The water going into the RO is split into 2 parts :

Part 1: This part goes into the membrane and undergoes the RO process. This output will be pure water of lower TDS.

Part 2: This water does not go through the RO membrane. It goes through a UF membrane or a UV Chamber, depending on the RO specification of RO+UV+TDS or RO+UV+UF. The output will be water which is pure, but of the same TDS as that of the input water.

The full output of the RO machine is a mixture of Part 1 + Part 2 water. The mixture is controlled through a valve connected to the Part 2 assembly, thus controlling the TDS.

This interestingly, is the main reason, why there is no RO+UV system and that a TDS controller with always be paired with a UV tube or a UF membrane. Attaching a UV tube to water which has already been processed through an RO system, will achieve nothing. But the water being added to control the TDS, needs some purification, because it is essentially raw.

So, in places where the input TDS value is low eg. TDS values of anything below 400, a TDS controller can help give you better tasting water.

 

The Myth Behind TDS Value

When RO salesmen or technicians come to your house to give you a demo about their product one of the first things they will do is check the TDS value of your water supply. But, what is TDS ?

TDS stands for ‘Total Dissolved Solids’. Which in turn means, it gives you an idea of hard your water supply is. The unit used in TDS meters is PPM (Parts per million). So a TDS value of 100 means it has 100 parts of solids dissolved in 1 million parts of water.

Now, PPM values when converted to mg/l format (milligrams per litre) remain roughly the same. So 100 PPM is roughly 100 mg/l. This information is important since all the standards mentioned in the WHO (World Health Organization) guidelines or in the BIS (Bureau of Indian Standards) documentation is given in mg/l.

Now you must be wondering, what is the WHO or BIS say about the ideal TDS of water ?

WHO : TDS below 1000 is okay for human consumption !

BIS : TDS below 500 is okay !

In case you think that the above data is wrong, check out the following links:

http://www.who.int/water_sanitation_health/dwq/chemicals/tds.pdf

http://bis.org.in/sf/fad/FAD25(2047)C.pdf

So, should you throw out your RO systems, or get a refund ? No, not quite yet.

The problem with TDS value is that it is only an indicator of how many minerals are dissolved. Not which minerals are dissolved. Just like a thermometer can tell you that you have a fever. But fever due to what ? That requires a blood test. To know what exactly is dissolved in you water requires a water report, typically done in a laboratory. So the TDS value in your home could be 300. Which is safe according to the WHO or BIS, but what if all that 300 TDS is mercury. Then what ?

So an RO system provides a middle solution. It brings the TDS value down to below 100. At these values, it does not matter much what is dissolved in the water as your kidneys will do the rest. Typically, a TDS of 70-90 is good value, as it provides safety and good taste. Very low TDS (<40) is typically not recommended as the human body also requires some minerals, especially in the summer season, when one tends to sweat a lot.

 

How does an RO system work ?

All RO systems, whether domestic or commercial, work on the same principle, namely the principle of Reverse Osmosis. There may be some add on’s as well depending on the system one buys eg. RO with TDS controller or RO + UV etc. But all in all, the purification is done through the RO process.

The best way to understand reverse osmosis is to first understand the natural process of osmosis. Osmosis is said to occur when a solvent flows from a region of higher concentration to a region of lower concentration through a semi-permeable membrane.

Quite a mouthful isn’t it ! Let me simplify it for you.

Think of it like this. You have a glass which is divided into 2 regions. One region has highly concentrated salt water and the other region has plain water. If you place a semi-permeable membrane (in this case, a membrane which allows only water molecules to pass through and not salt molecules) in between these 2 regions, water will flow from the plain water region to the salt water region, to equalize the water concentration on both sides. This happens automatically without the application of any external energy.

The reason why this happens is because of the 2nd law of thermodynamics. In case you are interested to read further, I encourage you check this out :

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics

Now when the water starts moving from one region to another through the membrane, it places some pressure on it. Just like when you use a sieve when pouring tea to catch the tea leaves, the sieve feels some pressure because of the tea moving through it. This pressure felt on the membrane during osmosis is called osmotic pressure.

In Reverse osmosis, we reverse this process. So, from salty water, we try and take out as much soft water as possible. The result is a small quantity of soft water and a larger quantity of even more salty water (called waste water). We achieve this by using a pressure pump and applying pressure on the membrane which is higher than the osmotic pressure. This way the water is forced through the membrane, which traps other particles and allows only water to pass through.

Think of the pump as the heart of the RO system and the membrane as the mind. The pump forces water through the membrane at high pressure to extract soft water from the hard water. The waste water which you get from an RO system, is not actually waste in the literal sense. It’s just water from which a quantity of soft water has been taken out leaving the remaining water even harder than before.

This is the basic principle of how an RO system works. Feel free to leave any question that you might have in the comments section and i’ll answer them to the best of my ability.