What kind of water to use?
 

I see many posts about using distilled or reverse osmosis water. I have just been using tap water, but I think I'm in a lucky area as far as water quality goes.

According to our water bureau the hardness is 3 to 8 parts per million. The sodium is 2 to 9 ppm. They also say that our pH is between 7.4 and 8.1, but I consistently measure it at between 6.0 and 6.4. So I'm not sure what that is about. No fluoride is added.

Overall I think I'm good on the dissolved minerals and pH front.

They do use chlorine and ammonia to disinfect the water. The water starts out pretty pure and never has the smell or taste of chlorine, so I think it is pretty low level as far as such treatments go. But I do wonder if that might be harmful to some of the delicate roots?

I haven't had any problems yet, but just wondered what other folks do.

You are lucky and your water sounds great. You can let a pitcher or bucket stand overnight so the chlorine evaporates. I have to use rain or RO because my total hardness is 205-291 ppm, sodium 27-98 ppm and total dissolved solids 388-1,390 ppm. pH is 7.1-8.0. However, my bones are probably great because I get a lot more calcium than most people!

Unless you are growing something that requires unusual water quality, your water should be fine.

Chlorine (usually reported as chloride, ppm or mg/L) is usually not a problem. Chloride is actually a plant micronutrient, one we rarely have to add.

It would be good to know the following; your water deparment probably measures them, but may not include in their public water reports. If you call or email them they can probably provide. The units of measurement are important, I've indicated the typical measurement units in parentheses, let me know if they are using something different:

Total dissolved solids or TDS (expressed as parts per million (ppm) or milligrams per liter (mg/L).

Electrical conductivity, EC, sometimes called specific conductance or specific conductivity. A surrogate for total dissolved solids (micro Siemens per centimeter - uS/cm; sometimes as umhos/cm)

Calcium (ppm or mg/L)

Magnesium (ppm or mg/L)

The combination of chlorine + ammonia makes chloramine, which is used by most water agencies for disinfection. (straight chlorine can react with organics to make trihalomethanes which can be carcinogenic, chloramine prevents that) Chloramine is a problem with fish, but not with plants. So no worries. It sounds like your city water is fantastic. Your orchids should love it. I am jealous...:)

My water is hard as nails well water so I use RO water and a fertiliser that is geared for that, at very low concentrations.

I have about 400 gal storage capacity for rain water plumbed into the gutters of my house.

Knowing about your water helps you to evaluate, and properly apply, information and advice that you receive. Based on the hardness and sodium values you have given, the dissolved solids are probably lower than the RO water that those of us in hard water areas get. Your water is very slightly acidic, right in the perfect range for orchids to absorb nutrients. If you buy fertilizer locally, it probably has been selected correctly. You will see advice to use "balanced" fertilizer (like 20-20-20, all three numbers the same) That's great if the water is hard and somewhat alkaline (my pH is about 7.8 where 7 is neutral) The middle number is phosphorus, a nutrient that orchids really don't need a lot of.. but it is in a compound that is rather acidic, helping to adjust the fertilizer water into a range that is correct for the plants. You would probably get a fertilizer with the middle number that is much lower. There are others on this forum that can give you much better information than I can about the details. But the lesson here is to put advice into context... what is the objective? How are your conditions different from those of the person giving the advice, and have they given enough detail for you to apply it?

The OP's water is slightly basic, not acidic, and being that the hardness is so low, I would highly suggest you use a fertilizer that contains both calcium and magnesium, as your water really has very little.

I was picking up "acidic" from Rothrock42's measurements of 6.0-6.4. The measurements from the water bureau are indeed slightly basic. That water is so pure, that very little dissolved CO2 from the air could shift it that much because there's no buffering from solids. Straight out of the tap it's that low, let it sit for an hour or so to warm up, and it's closer to what the water district states. You are so right to point out that some calcium and magnesium need to be added.

I am responding to the OP, and pretty much skipping over all the responses.

Being in the Pacific Northwest on the West slope of the Cascades, your municipal water probably originates from snow pack, rain and/or rivers, not ground water pumped from wells that has leached minerals from the ground. There are exceptions to that. Bothell, Wa. used to have the most gawd-awful smelling and tasting water I had ever run into as a kid, a strong iron taste to it.
EDIT:
Now that I think about it, it was at my grandparent's place 60 or more years ago. They may have had their own well back then.

Most municipal water utilities buffer their water to make it slightly basic to control corrosion in the piping system.

While my information is dated, I grew up in the PNW, but haven't lived there for over 35 years now. I assume that some of the best municipal water in the lower 48 is still found in the PNW.

My experience with using high quality municipal water [glacial runoff in Alaska] on orchids is to not worry about it. If chlorine does concern you, draw the water and let it stand for a few hours. The chlorine will dissipate. Treat the orchids as if you were using rain water by making sure they are getting all the minerals they need with their fertilizer.

I still have access to high quality water. I now live in a high rainfall area and have a 10k gallon catchment tank for our household water.