Dialing in whole house RO system - corrosive water leeching pipes

[bees4thees]

Have a whole house commercial RO system from Canature. It has one membrane and a 300gal holding tank on it.

I’m on a well. Before the RO the water goes through a sediment filter, iron reducer then softener. After a chemical injection pump with 30 gal brine tank adds Neutra 7 soda ash to raise the ph, it goes through a radon aerator and finally through a UV filter then to the house.

Problem is I can’t get the injection dialed in, the water is still corrosive even with a pH of between 7-8, showing about 3ppb lead and 0.17ppm copper. The water has a metallic taste.

The other problem I’m having is the solution tends to settle and collect in the injection brine tank. I have to mix it every couple of weeks to keep it all suspended. This is happening even at a 4% solution with the soda ash (neutra 7).

My house has copper pipes with lead solder.

How can I get this system dialed in and balanced?

 

[bimr]

RO produces corrosive water because it allows the carbon dioxide to pass through but removes the scale forming cations, magnesium and calcium. The water softener makes the situation even worse, but may prevent scaling of the RO system.

Consider blending a portion of the raw water around the water softener. Consider adding a calcium carbonate feed.

Investigate the Langelier Index. pH is not the sole factor in corrosion.

Post a complete water analysis for further discussion.

 

[bees4thees]

Thank you very much. The recent test I have shows only lead/copper but I have one from earlier this year. It was when the ph was a little higher, in the 8s. Currently it's in the low 7s when I had this test done.

Prior test:

https://gosimplelab.com/Q6EBPX/all-results

The lead and copper were much lower. My theory is since there's almost no hardness, according to how LSI is computed I would need to add more pH / alkalinity to make up for it which might explain why it was better at a higher pH before.

To clarify, the order of the whole system is this:

- Well pump (source water)
- Sediment filter
- Iron reducer
- Softener
- RO
- Neutra 7 injection
- Radon aeration
- UV light

 

[coloeng]

The action levels for lead and copper in drinking water, according to the Safe Drinking Water Act, are 15 ppb and 1.3 ppm, respectively. While ideally you would like to get both of those to zero, the 3 ppb and 0.17 ppm don't seem that unrealistic if you have copper pipes with lead-based solder.

 

[EdStainless]

blending a small amount of the softened water would likely do the trick.
Adding the injection of Ca carbonate would also, but that would be another chemical to manage.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[bimr]

You seem to be on the right track.

I don't think you should blend softener effluent as the effluent will have no scale forming hardness. You need the hardness to increase the Langelier value.

Why do you think you have lead solder? Lead solder was phased out some years ago.

 

[bees4thees]

House was built in 79 and a lead test kit confirmed lead on one of the solder joints.