I am offering this thread as a Sticky based on a recent post in which a first time all grain brewer made many of the mistakes listed here. Most of these mistakes result from adherence to recommendations from old brewing references. In the last 5 years or so we have learned a lot about how to manage brewing water and slain a few sacred cows in the process.
1) Don't do anything to your water until you know what is in it. If you don't have a valid water ion content report get one from your supplier or by sending a sample to Ward Labs. In the interim use RO water from the health food store (or wherever) and follow the guidance at https://www.homebrewtalk.com/showthread.php?t=198460
2) Don't rely on pH test strips in making decisions concerning the addition of alkali or acid to mash or brewing water. They simply aren't accurate enough. Obtain a good pH meter (far and away the best) or at least get an estimate of mash pH from one of the calculators/spreadsheets.
3) Don't add alkali (chalk, bicarbonate, lime...) to mash or brew water until you have verified, preferably by measurement, that it is actually necessary. Do not rely on the beer's color for guidance on how much alkali to add. If you can't measure a test mash then use a calculator but be aware that these sometimes call for alkali additions when they are not necessary.
4) Don't use chalk as a source of alkali. It does not react fully for days and continues to add alkalinity to your wort even into the fermenter. This is not a good thing.
5) Don't rely on 'mash pH stabilizers'. These do not work. All they do is add sodium to your beer (and phosphate ions).
6) Don't assume that because a container is labeled 'calcium chloride' that it contains 100% calcium chloride nor that a container labeled 'lime' contains 100% calcium hydroxide. The former picks up water from the air (even during the brief times it is open while you are removing material from the container) and the latter picks up carbon dioxide from the air. See https://www.homebrewtalk.com/showthread.php?t=501377 for how to handle calcium chloride. Ask on Brew Science about how to handle lime if you want to use it.
7) Don't be a slave to profiles nor assume that there is an ideal water chemistry for a particular beer but rather understand that a satisfactory representation of a particular style can be had with waters that are appreciably different from one another as long as they have the same general qualities as the water on which the beer is based. The satisfaction with a style is a matter of personal preference (taste).
8)Don't assume that the ratio of chloride to sulfate ion content is a proxy for some malty - hoppy scale. There are two degrees of freedom here and you must learn what the effects of each ion on beer flavor are and adjust them to suit your tastes (or those of your customers).
I don't expect much argument about any of these except perhaps #8. The validity of the ratio persists in some people's minds. You can, of course, always keep track of the ratio (the concentration of one salt and a ratio is two degrees of freedom and as long as you are aware that there are 2 DOF or even that a large number of people think that there are 2 DOF you should be OK).
Finally a "Do": Do drop in on Brew Science from time to time where topics related to these items are all under pretty continuous discussion.
And another "Do": Do be aware that all beers require acid in some form in order to reach a mash pH in the desired range of 5.3 - 5.6 as measured at room temperature. In some cases the specialty malts can supply it but in general it will have to be supplied by the brewer usually in the form of lactic acid, phosohoric acid or acidulated malt.
1) Don't do anything to your water until you know what is in it. If you don't have a valid water ion content report get one from your supplier or by sending a sample to Ward Labs. In the interim use RO water from the health food store (or wherever) and follow the guidance at https://www.homebrewtalk.com/showthread.php?t=198460
2) Don't rely on pH test strips in making decisions concerning the addition of alkali or acid to mash or brewing water. They simply aren't accurate enough. Obtain a good pH meter (far and away the best) or at least get an estimate of mash pH from one of the calculators/spreadsheets.
3) Don't add alkali (chalk, bicarbonate, lime...) to mash or brew water until you have verified, preferably by measurement, that it is actually necessary. Do not rely on the beer's color for guidance on how much alkali to add. If you can't measure a test mash then use a calculator but be aware that these sometimes call for alkali additions when they are not necessary.
4) Don't use chalk as a source of alkali. It does not react fully for days and continues to add alkalinity to your wort even into the fermenter. This is not a good thing.
5) Don't rely on 'mash pH stabilizers'. These do not work. All they do is add sodium to your beer (and phosphate ions).
6) Don't assume that because a container is labeled 'calcium chloride' that it contains 100% calcium chloride nor that a container labeled 'lime' contains 100% calcium hydroxide. The former picks up water from the air (even during the brief times it is open while you are removing material from the container) and the latter picks up carbon dioxide from the air. See https://www.homebrewtalk.com/showthread.php?t=501377 for how to handle calcium chloride. Ask on Brew Science about how to handle lime if you want to use it.
7) Don't be a slave to profiles nor assume that there is an ideal water chemistry for a particular beer but rather understand that a satisfactory representation of a particular style can be had with waters that are appreciably different from one another as long as they have the same general qualities as the water on which the beer is based. The satisfaction with a style is a matter of personal preference (taste).
8)Don't assume that the ratio of chloride to sulfate ion content is a proxy for some malty - hoppy scale. There are two degrees of freedom here and you must learn what the effects of each ion on beer flavor are and adjust them to suit your tastes (or those of your customers).
I don't expect much argument about any of these except perhaps #8. The validity of the ratio persists in some people's minds. You can, of course, always keep track of the ratio (the concentration of one salt and a ratio is two degrees of freedom and as long as you are aware that there are 2 DOF or even that a large number of people think that there are 2 DOF you should be OK).
Finally a "Do": Do drop in on Brew Science from time to time where topics related to these items are all under pretty continuous discussion.
And another "Do": Do be aware that all beers require acid in some form in order to reach a mash pH in the desired range of 5.3 - 5.6 as measured at room temperature. In some cases the specialty malts can supply it but in general it will have to be supplied by the brewer usually in the form of lactic acid, phosohoric acid or acidulated malt.