I was having issues with high PH water averaging in the low 8s. If you have a large collection of sensitive PH/tap water plants. It may be wise to invest in a RO water system, which CoPlantNut mentioned for removing unwanted additives to the water.
There are workarounds even with blueberries, (making selections on PH tolerance, ex. 'Sunshine Blue' Blueberry). I was adding vinegar to the watering schedule but found it only to mainly help the blueberries much. Foliar spraying seemed to correct a lot of nutrient issues/slow growing caused by the water.
I figured if I started with a acidic container soil mix, the end result would be balanced with the water added. Now using a mainly pine bark mix with foliar spraying, I am now getting great results even with the tap water.
I always start with an acidic soil mix (for plants that want that) but if you keep watering that mix with PH 8.0 water, the PH will slowly creep up to match the water. The water keeps replenishing the alkaline buffering agents with every watering, and eventually the soil mix will become alkaline. Try getting a soil analysis done on an "acidic" potting mix after it had been watered with tap water for a couple years-- that's what changed my mind. Really, the only way to maintain an acidic soil mix is by replacing it frequently or by adjusting the PH of the water you're using. How long a mix will remain acid depends on the PH of your water and exactly what chemicals are in your water to make it alkaline in the first place-- some are better at buffering (raising the PH over a long term) than others.
I've grown plants that prefer acidic conditions for years; most do just fine with tap water, even as it makes their soil alkaline. Blueberries and miracle fruit are the only fruits I'm growing that seem to demand acidic conditions, but my carambolas and Eugenias seem happier now that they are always getting PH 5.5-6.0 water. (My carambola refuses to bear fruit, however...)
Kevin
Kevin,
No question after a while the PH of the soil mix creeps up. I still add vinegar but only hand water like this a couple times during the summer and fall (when I am dependent on tap water 100%). I try to replace the soil mix every 2-3 years, by this time the mix has broken down quite a bit. Mulching with fresh pine bark is done a couple times a year.
Old soil mix is leeched out and composted, used for in ground beds. I have found out the hard way in the past, that anything from the Amazon despises tap water; Acai palm, Cupuacu, etc.
Plants with the minimal issues of tap water; pomegranates, mulberry, apples, cacti (including dragon fruit), wax jambu, most bananas.