That depends on the tap water, if yours is "hard" it contains significant mineral contact. The presence of iron is bad, copper even worse.
Where I am (Maryland) the tap water is pretty soft; still, I use only distilled water (grocery store) to make up electrolyte and dye solutions. I use tap water for rinsing with no ill effects.
I'm assuming that you found an appropriate thermometer, and are now anodizing in a 70 -75 deg. F. range.
I'm not real clear on the actual electrolyte concentration you are going to use; if your going to operate in the 3 to 6 A/sq.ft. range LCD) you should be using 1:3 battery acid to water. Above 6 to about 15 A/sq.ft. use 1:2 battery acid to water.
BTW, personally I like 6 A/sq.ft. the best for LCD.
The 720 Rule is quite reliable, something else is going on. The wrong acid ratio for the current density will make trouble, degrading connections can easily cause failures and usually does.
You may not have COMPLETELY removed the natural oxide from the work, doing this chemically isn't as easy as it sounds. Thoroughly sanding a test sample to be sure the oxide is removed would be a good test to see if this is going on.
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