How about using RO Water @ Reverse Osmosis water.. It has no mineral contents.. It's the closest water type to distilled water

Who says batt water cant use?

Limescale build up is the last thing you want, You must use deionised or distilled water. You can buy this very cheaply from a car spares shop, as “car battery top-up water”.

If your system uses more than one kind of metal in its construction, (and it almost certainly will) then they will form a crude battery. This can cause the more reactive of the two metals to corrode. You can avoid this by adding Zerex, Purple Ice or Water Wetter. Only a small capful is enough for most systems. Consult the additive's instructions for the correct ratio.

Water Cooling Liquid
A final yet important consideration to make is liquid coolant type. Theoretically, you could fill your water cooling system with anything, but some fluids work much better than others. First of all, do not use tap water. Tap water has minerals, bacteria, and algae in it which will corrode and cloud your water cooling system, possibly causing a catastrophic failure. Another alternative is de-ionized water. De-ionized or non-conductive water may seem desirable initially, because it is a poor electrical conductor, and therefore will not cause much damage if a leak occurs. However, water is an excellent solvent, and so if de-ionized water is put into a water cooling system, it will corrode the water blocks to get its ions back. Therefore, de-ionized water is not something we recommend, either.
A good choice is distilled water, because it is relatively cheap yet pure enough to use in a water cooling system. Distilled water will not deposit harmful minerals in your system, nor will it cause algal blooms because there are no living organisms present. It will not, however, corrode your water blocks because it is not de-ionized. There are various additives which may be added to the coolant in your system. Water wetter is great for increasing the cooling capacity of your system by altering the properties of water and making it even more thermally capacitive. Water wetter will also help reduce corrosion in your water cooling system. Other additives, such as UV-reactive dyes, may be added for aesthetic reasons.

u can get distilled water from petronas la .
i bought 5 litre for RM7 .
u see d table of nutrient , its all 0 . so its distilled ^^,
somtimes they juz print out as drinking water so u check d nutrient .

deionised water is better as coolant compare to distlled water... just the problem with batt water is abit acidic and may corrode the radiator after long run...

so in the end, what to use as the liquid in ur WC?