The main reason that there's a standard for pH in the regulations is that water with low pH can be corrosive to metal plumbing.
This means the water can contain excessive concentrations of metals like copper, nickel, zinc and lead.
Signs that corrosion is taking place include excessive leaks and staining of sanitary ware (often green where there's copper).
High pH water can cause taste problems, corrode metal pipes and irritate skin.
How pH correction works
Treatment to increase pH usually involves passing water through a neutralising filter containing alkaline media such as limestone or magnesium oxide. You should get advice from an installer.
It's important that the filter's size, and the blend of media within it, is right for your water supply, otherwise the pH could be under, or over, corrected.
Installing a neutralising filter correctly depends on your individual circumstances, so it's best to consult a specialist contractor.
Neutralising filters should generally be fitted after any other filtration, so that the media does not become clogged by debris.
Neutralising filters rely on alkaline media dissolving in the water to change the pH.
The media is gradually used up in the process, and will eventually need to be replaced.
It is important that the amount of media in the filter is regularly checked. This can be done by monitoring pH using a simple test, and seeing if there are any stains on fittings and sanitary ware.
If you do need to top up the media, make sure you use the right type. It is worth cleaning out the filter vessel from time to time and completely changing the media.
Alkaline media can be very corrosive, so it's best to follow your manufacturer's instructions, or get help from a professional.