Excellent info from enprise, precise and to the point. Although I mostly agree with the info he has provided, I must say that if you choose to drink the tap water, tread with caution! remember, Latin America doesnot for the most part flush it's toilet paper. Most small town have primitive water resources, and couple this with the countless dead dogs you will discover along the way, all this washes into the aquafer and ultimately ends up in the water. See what the locals are drinking before drinking it yourself. A 25 litre bottle of water costs roughly twice as much as a 1 litre bottle, so you will find that safe water is easily accessible, just ask a resturaunt owner to fill your bottle and give him one or two pesos if they ask, which they usually don't. After living here for a number of months ans currently travling for the last month, I have yet to buy a bottle of water but drink my fill every day.

As Ron says , the tap water may not be quite what you expected it to be.
Aquifer contamination is a consideration but not the main culprit. Most of the newer Mexican and CA municipal water sources are quite good but it is what occurs after the water leaves the municipal mains which causes the problem.
There is a persistent problem of water pressure loss and inadequate volume . To overcome this nearly all houses and hotels in Mexico are equiped with header tanks on the roof. Water from the city main is run directly into the small tanks on private houses but at the large buildings like hotels the lift to the roof and the required volume is too great . Therefor they run the city water into a large in-ground cistern and from there use their own electric pumps to move it up. These in -ground cisterns are often in the floor of the entry way , the parking lot or... ... and are very often left with lids off so that dirt, rain runoff and other crud can get in. Many places they burn the used toilet paper and if it is windy this wonderful stuff gets blown around the yard and guess where ! Then on the roof tanks, hotels and private houses, the lids are usually lost so that birds and other wildlife can bathe and drown etc in them. You get the picture
If you are at hotels they usually supply a jug of drinking water in the hall or lobby. Fill your own bottles here. Some higher end places have their own extra chlorination equipment and have labels on their taps indicating thus.
I have always had no problem using tapwater in my own bottles then adding 2 drops of chlorine bleach for each liter, let stand 30 min. Make enough to last all day for drinking and washing fruit.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93

This is what I was needing to hear.

Thanks again!