My personal rule of thumb: if I can't find the answer to that or similar situational circumstances, then they've left that up to the GM's discretion, on purpose or not.
I don't have my copy handy, so I can't quote RAW right now, but I do believe there is a mention about the liquid volatility either in the overall dungeon description or the room specifically. At least in my copy of the Anniversary Edition.
There are also several hilarious/frightening uses for the liquid posted thru out the Boards here. I'd try the sticky for book 1 first.
I had a player planning on building Sinspawn Grenades. I talked him out of it by pointing out Nualia had escaped them and she knew about the pool.
That said, I'd rule the Runewell water loses its potency when a mile away from the Runewell. The other? You could have it degrade into regular unholy water or leave as-is.
The waters from the Altar of Lamashtu becomes normal unholy water after an hour if I recall correctly. I'm not sure about the Runewell.
My players took samples of the Waters of Lamashtu (they have since used them)...one player failed a check for gathering and suffered ability damage to dex (a slightly crippled hand) and int (minor insanity). He roleplayed it pretty well...
When they entered Erylium's room, he claimed the runes on the wall said that the water they had gathered would allow them to control her if they could hit her with it. The group was amazed he could read the runes. Later, while fighting Erylium he decided that the Runewell must have healing properties so he submerged his hand into it. Chaos erupted after that...as the rest of the party was fighting Erylium outside the room and he proceeded to head out there in a rage, saw the party fighter first and attacked him (this character was new to the group, having replaced the fighter that had previously died). The fighter turned to defend himself and struck down the offending PC...the rest of the party saw this attack, and only this attack so the distrust that followed was a very interesting development.
They have since killed Erylium and deactivated the Runewell...I'm quite amazed that no one decided to gather some of it's water, but after their experience with the Waters of Lamashtu I guess they thought the risk vs reward wasn't really there.
