Testing tap water to determine if RO/DI is needed..

Well, all I can say is that I've been reefing now for just over 18 years, and I started out with tap water.
After about 5 years, I got a computer and found out I should not use tap water so I began using DI and kept on that for 2 years.
I didn't see any difference in any of my tanks so I went back to tap water for another year before returning to DI again for one more year.
With no differences showing again, I have used nothing but tap for the last 9 years now.
I think there is tap water good enough out there but I can't say as to how you find it.
We are on Great Lakes water and London appears to have an excellent treatment plant.
I have three 55g olive barrels that I aerate and age the water for at least overnight or longer to dispel the chlorine London uses.
When I started and for years after, everyone around here used tap water.
Now, some use it but the majority have switch to the RO/DI and yet I don't see differences in the tanks that do and those that don't, other than choice of inhabitants and the ways they are aquascaped.
I see tanks with treated water that are full of hair algae and untreated that have no problems.
It makes me wonder how many other tanks in other areas could be going without treated water, but everyone has just jumped on the bandwagon for treated water due to those that actually do need it.
I've never ever tested for TDS.

 

One of the biggest problems with tap water is you have no control over its quality or its stability.

Say a major storm blows through, treatment changes as does final water quality. They add more chemicals to remove the turbidity and the pH and overall quality will change.

Or another issue is distribution system quality. Joe Contractor down the street digs in to the water main and causes a major leak. Of course the closest valves are flooded out so they must go back a couple streets to the next valves so you now have a major problem. You have not been outside to see the problem and you make a huge batch of water for a water change or your ATO tops off the sump automatically. You just experienced a backflow incident and sucked contaminated water in to your system and your home.

Or your utility recently came under fire for lead and copper violations so without your knowledge they begin adding sodium hexametaphosphate for corrosion control and adjusting the pH of the water leaving the plant. You now have a phosphate issue and didn't even know it.

Or they have decided free chlorine is not sufficient anymore since it does not reach the far ends of the distribution system and they are getting bad bacteria samples. They switch to chloramines. Normal dechlorinators do not touch the ammonia portion of chloramines nor does carbon filtration. You now have an ammonia issue and could upset your system.

The point is, you have no control over tap water and it can and does change always.
With RO/DI you have ultimate control over your water quality and it is stable, you get the same product each and every time no matter the weather or tap water conditions.

You may "get away" with tap water for awhile or maybe even forever, but that one "gotcha" can be a disaster. For a $120 investment it is extremely cheap insurance and peace of mind.

 

For me, it's a lot more cost than just the equipment.
I would have to dump the bypass water, having no place to store the volume produced by what I use, and I couldn't use all that amount on other things anyway.
The cost of paying for the discarded water at the rates they now charge, and, the fact that many other charges, like infrastructure and replacement charges, are based on total water usage, it would probably double my already high water costs.
Fortunately here in London, they won't make changes like chloramines instead of chlorine without it being publicly noted first. Even when they changed the pH to lessen the lead content due to dissolve piping, they advised in the papers and media ahead of time.

 

People are often misled on how much their water and sewer costs are with a RO/DI system.
Here in Phoenix with water rates between 2.86 and 4.19 per 100 cubic feet (748 gallons) and sewer at $2.30 per 100 cu ft and based on 90% of your winter months usage, it still works out to less than a nickel a gallon including the waste flows which I send to the sanitary sewer to be recycled.
Its not a lot of money compared to the risk of using tap water or the hassle of hauling purchased water. I am here to tell you, it will bite you one day and maybe even drive you out of the hobby. This is unfortunate but happens every day all over the world and probably the biggest reason people get out of the hobby. It doesn't matter if you are in Canada, the US or Europe, its all the same.

 

In my case I think 18yrs now the odds are in my favour.
I should have added that you have VERY cheap water compared to me.
Also, once the extra charges based on consumption are added, the bill triples.

 

You can't argue with AZDesertRat.. He is not only the most knowledgeable person of this subject on this forum, but on many other major forums as well. He should write a book. I totally agree that "it will bite you one day and maybe even drive you out of the hobby." However, I think that it is actually biting you today as well (your "algae galore). It will continue to bite you worse and worse in the future as the contaminants build up in your system. There is no need to get a report. Get a TDS meter. Even without a TDS meter, I can guarantee that your TDS is not 0 (which is what the water you are adding to your reef tank should be).