Before you add that water to your battery, do you know where it came from and where it has been? The fastest way to damage your battery is to add contaminated water. There two requirements that must be met?

1. Water must be demineralized.
2. Water must be deionized.

Tap water is around 250 to 500 microSiemens (mS). Battery water should never exceed 10 mS. Only use equipment in which the battery water cannot come into contact with metal, otherwise it will immediately be ionized.

Both requirements can be easily met using Distilled Water. But make sure the water does not become contaminated once you open the bottle. Like using a metal funnel.