Still if you can get your pet shop to do a hardness or TDS (total Dissolved Solids) test, that may give you a hint.
1	Still	still	ADV	RB	_	24	advmod	24:advmod	_
2	if	if	SCONJ	IN	_	5	mark	5:mark	_
3	you	you	PRON	PRP	Case=Nom|Person=2|PronType=Prs	5	nsubj	5:nsubj	_
4	can	can	AUX	MD	VerbForm=Fin	5	aux	5:aux	_
5	get	get	VERB	VB	VerbForm=Inf	24	advcl	24:advcl:if	_
6	your	your	PRON	PRP$	Case=Gen|Person=2|Poss=Yes|PronType=Prs	8	nmod:poss	8:nmod:poss	_
7	pet	pet	NOUN	NN	Number=Sing	8	compound	8:compound	_
8	shop	shop	NOUN	NN	Number=Sing	5	obj	5:obj|10:nsubj:xsubj	_
9	to	to	PART	TO	_	10	mark	10:mark	_
10	do	do	VERB	VB	VerbForm=Inf	5	xcomp	5:xcomp	_
11	a	a	DET	DT	Definite=Ind|PronType=Art	20	det	20:det	_
12	hardness	hardness	NOUN	NN	Number=Sing	20	compound	20:compound	_
13	or	or	CCONJ	CC	_	14	cc	14:cc	_
14	TDS	tds	NOUN	NN	Number=Sing	12	conj	12:conj:or|20:compound	_
15	(	(	PUNCT	-LRB-	_	18	punct	18:punct	SpaceAfter=No
16	total	total	ADJ	JJ	Degree=Pos	18	amod	18:amod	_
17	Dissolved	dissolve	VERB	VBN	Tense=Past|VerbForm=Part	18	amod	18:amod	_
18	Solids	solid	NOUN	NNS	Number=Plur	14	appos	14:appos	SpaceAfter=No
19	)	)	PUNCT	-RRB-	_	18	punct	18:punct	_
20	test	test	NOUN	NN	Number=Sing	10	obj	10:obj	SpaceAfter=No
21	,	,	PUNCT	,	_	24	punct	24:punct	_
22	that	that	PRON	DT	Number=Sing|PronType=Dem	24	nsubj	24:nsubj	_
23	may	may	AUX	MD	VerbForm=Fin	24	aux	24:aux	_
24	give	give	VERB	VB	VerbForm=Inf	0	root	0:root	_
25	you	you	PRON	PRP	Case=Acc|Person=2|PronType=Prs	24	iobj	24:iobj	_
26	a	a	DET	DT	Definite=Ind|PronType=Art	27	det	27:det	_
27	hint	hint	NOUN	NN	Number=Sing	24	obj	24:obj	SpaceAfter=No
28	.	.	PUNCT	.	_	24	punct	24:punct	SpaceAfter=No
