If it is tap water you plan on using then it should really be filtered either by reverse osmosis, or through an activated carbon or ionic filter. This is primarily to remove the chlorine/chloramines which would kill micro-organism in your soil that you want to be there to stabilize the pH and make nutrients more available/provide them to the plant. Filtration will also remove excess mineral salts that could potentially interfere with nutrient up-take. The contents of tap water will vary wildly depending on your location and besides chlorine it might incl
- fluoride
- arsenic
- cyanide
- radium
- aluminium
- copper
- lead
- mercury
- cadmium
- chromium
- barium
- beryllium
- antimony
- selenium
- thallium
- Trihalomethanes
- Haloacetic Acids
- Pesticides
- Hormones
When it comes to filtration there are a few options:
Reverse osmosis filtration systems are the most expensive. Some models come with activated carbon and prefilters to increase efficiency and extend the life of the membrane. These can remove anywhere between 95-99% of contaminates and to the best of my knowledge also filter out potentially unwanted micro-organism as well as fluoride.
De-chlorinators/sediment filters such as the Hydro-logic Small/Tall Boy De-chlorinators removed up to 99% of chlorine and 90% of sediment. These systems have both a carbon filter to remove the chlorine and a sediment filter. They are fairly efficient when maintained properly, the Small Boy for instance is capable of filtering 60 gallons per hour.
Table-top (pitcher) tap water filtration systems: notably Brita, Pur, ZeroWater:
Brita and Pur pitchers are smaller activated carbon filters with ion exchange resin. These are the cheapest units available and they do effectively remove most chlorine/chloramines from tap water. These will not remove fluoride. I know that the Brita filters are supposed to be able to process something like 40 gallons of water, then the filter needs to be changed. It is very important to change the filters on these units when they cease to filter efficiently.
ZeroWater is a five-stage activated carbon and ionic filter. These [allegedly] completely remove all dissolved solids in tap water, including fluoride. They even come with a TDS meter that can measure from 000-999 parts per million. I have been using mine for about a week now, which I purchased at Target for less than $30. My tap water goes in at 068 ppm and comes out 000 ppm. Even water from a Poland Spring bottle measured 024 ppm.
So far I am quite impressed, even though it filters very slowly. But, if it didn't filter slow it probably wouldn't be as efficient as it is. The filter is supposed to be changed when it starts to read 006 ppm. The manufacturer requests they be mailed back to them for recycling in exchange for a $5 coupon off the next two filters.
A note about all carbon filters: The water MUST BE COLD in order for the chlorine to be removed. NEVER EVER try to filter warm or hot water through an activated carbon filter. I am pretty sure that doing so could actually end up leaching chlorine from the filter
INTO the water that comes out.
After you filter the water you can add in a little bit of Cal-Mag or something similar to bring the ppm up to around 150. Whatever else you add depends on your feeding regimen and the needs of your plants.
You don't really
have to pH your water if you're growing in soil organically. In fact, pH UP (potassium hydroxide) may also adversely affect beneficial soil microbes.